bug#63840: 29.0.91; c-ts-mode fails to fontify common C extension

[Po Lu]

A common extension to the C language is the use of the `$' sign inside
external identifier names.

This is permitted by GNU CC on most systems it supports, and also
supported by CC Mode.  However, it does not work on c-ts-mode:

sl$loadarena ()
{
  struct FAB fab;
  register int status;
  extern char *sl$dfname;

  fab = cc$rms_fab;
  fab.fab$b_fac = FAB$M_BIO | FAB$M_GET;
  fab.fab$l_fna = sl$dfname;
  fab.fab$b_fns = strlen (sl$dfname);
  status = sys$open (&fab);
  if (status != RMS$_NORMAL)
    return status;
  /* More code below.  */
}

in the identifier name of this function declarator, `sl' is fontified as
a type.  `$' is not fontified at all.  `loadarena' is fontified as an
identifier name, as it should be.  In:

  extern char *sl$defname;

only `dfname' is fontified as a variable name; in CC Mode, all
fontification is correct.

This should be a simple change in c-ts-mode's identifier fontifying
regexp to include `$', right?  I don't know enough about tree-sitter to
fix it myself.

Thanks.