bug#45557: 27.1; Incorrect rendering of COMBINING OVERLINE

[Stephen Eglen]

> If you move the cursor to x̅, does Emacs display a single cursor block
> that includes both x and the overline, or does it behave as if those
> were 2 separate glyphs?  If the latter, what does Emacs show in the
> *Help* buffer if you go to the ̅ glyph and type "C-u C-x ="?

It appears as two separate glyphs.  The first is char "x" (decimal 120)
and then the second is given as below

position: 86 of 87 (98%), column: 3
            character: ̅ (displayed as ̅) (codepoint 773, #o1405, #x305)
              charset: unicode-bmp (Unicode Basic Multilingual Plane 
(U+0000..U+FFFF))
code point in charset: 0x0305
               script: latin
               syntax: w        which means: word
             category: ^:Combining
             to input: type "C-x 8 RET 305" or "C-x 8 RET COMBINING OVERLINE"
          buffer code: #xCC #x85
            file code: #xCC #x85 (encoded by coding system utf-8-unix)
              display: by this font (glyph code)
    ftcrhb:-UKWN-JuliaMono-normal-normal-normal-*-19-*-*-*-m-0-iso10646-1 
(#x1F1D)

Character code properties: customize what to show
  name: COMBINING OVERLINE
  old-name: NON-SPACING OVERSCORE
  general-category: Mn (Mark, Nonspacing)
  decomposition: (773) ('̅')

There are text properties here:
  fontified            t

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