bug#64056: 28.2; CPerl mode: bad coloring when a comment block is used

[Vincent Lefevre]

When a comment block is used, i.e.

=begin comment

[code to comment]

=end comment

=cut

as described in the perlfaq7 man page, after some edition, everything
starting at the "=begin comment" line is in the comment color, even
the code after the "=cut" line (which is no longer commented code).

To reproduce the bug:

1. Create a file with

----------------------------------------
#!/usr/bin/env perl

foo;

=begin comment

bar;

=end comment

=cut

print "OK\n";
----------------------------------------

2. Open it with "emacs -Q".
3. M-x cperl-mode
4. Go to the beginning of line "foo;".
5. C-k
6. Go to the beginning of line "bar;".
7. C-y

At step 7, the color of the line

  print "OK\n";

changes to the comment color.

This occurs whether the Emacs X11 interface is used or not.
And this bug is still reproducible with cperl-mode.el from
the Git master branch.

My Debian bug report:
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1037544


In GNU Emacs 28.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.37, cairo 
version 1.16.0)
 of 2023-05-14, modified by Debian built on x86-ubc-01
Windowing system distributor 'The X.Org Foundation', version 11.0.12101007
System Description: Debian GNU/Linux trixie/sid

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/libexec
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-libsystemd --with-pop=yes
 
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/28.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/28.2/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils
 --with-native-compilation --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/libexec
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-libsystemd --with-pop=yes
 
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/28.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/28.2/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils
 --with-native-compilation --with-cairo --with-x=yes
 --with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -ffile-prefix-map=/build/emacs-mPr7Vr/emacs-28.2+1=.
 -fstack-protector-strong -Wformat -Werror=format-security -Wall'
 'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES
NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF
TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM GTK3 ZLIB

Important settings:
  value of $LC_COLLATE: POSIX
  value of $LC_CTYPE: C.UTF-8
  value of $LC_TIME: en_DK.utf8
  value of $LANG: POSIX
  locale-coding-system: utf-8-unix

Major mode: CPerl

Minor modes in effect:
  display-time-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-11/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-11/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-11/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-12/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-12/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-12/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-13/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-13/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-13/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-14/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-14/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-14/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-15/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-15/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-15/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-3.5/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-3.5/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-3.5/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-3.6/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-3.6/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-3.6/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-3.7/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-3.7/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-3.7/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-7/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-7/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-7/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-8/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-8/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-8/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-9/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-9/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-9/tablegen-mode
/usr/share/emacs/site-lisp/elpa/po-mode-0.21/po-mode hides 
/usr/share/emacs/site-lisp/elpa-src/po-mode-0.21/po-mode
/usr/share/emacs/site-lisp/elpa/po-mode-0.21/po-mode-pkg hides 
/usr/share/emacs/site-lisp/elpa-src/po-mode-0.21/po-mode-pkg
/usr/share/emacs/site-lisp/elpa/po-mode-0.21/po-mode-autoloads hides 
/usr/share/emacs/site-lisp/elpa-src/po-mode-0.21/po-mode-autoloads
/usr/share/emacs/site-lisp/latex-cjk-thai/thai-word hides 
/usr/share/emacs/28.2/lisp/language/thai-word

Features:
(shadow sort mail-extr warnings emacsbug message rmc puny dired
dired-loaddefs rfc822 mml mml-sec epa derived epg rfc6068 epg-config
gnus-util rmail rmail-loaddefs text-property-search time-date mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
cperl-mode rx facemenu cus-edit pp cus-start wid-edit time cus-load
cc-styles cc-align cc-engine cc-vars cc-defs edmacro kmacro mmm-auto
mmm-vars mmm-utils mmm-compat package browse-url url url-proxy
url-privacy url-expand url-methods url-history url-cookie url-domsuf
url-util mailcap url-handlers url-parse auth-source cl-seq eieio
eieio-core cl-macs eieio-loaddefs password-cache json subr-x map
url-vars seq byte-opt gv bytecomp byte-compile cconv cl-loaddefs cl-lib
iso-transl tooltip eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode mwheel term/x-win x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock
font-lock syntax font-core term/tty-colors frame minibuffer cl-generic
cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese composite emoji-zwj charscript
charprop case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice button loaddefs faces cus-face macroexp files
window text-properties overlay sha1 md5 base64 format env code-pages
mule custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
cairo move-toolbar gtk x-toolkit x multi-tty make-network-process
native-compile emacs)

Memory information:
((conses 16 135608 6639)
 (symbols 48 11538 0)
 (strings 32 34682 2270)
 (string-bytes 1 1172324)
 (vectors 16 16884)
 (vector-slots 8 353839 7492)
 (floats 8 46 11)
 (intervals 56 297 0)
 (buffers 992 12))