[vim/vim] Wrong display width for U+24C2 CIRCLED LATIN CAPITAL LETTER M (Issue #20989)

zahlman created an issue (vim/vim#20989)

### Steps to reproduce

With Vim configured to use UTF-8:
```
echo ⓁⓂⓃ > test.txt
vim text.txt
```

### Expected behaviour

The circled letters should appear next to each other, each occupying a single terminal cell, as they do on the command line.

Instead, a space appears after the Ⓜ, as if it had been incorrectly detected as a "wide" character. This only appears to affect M and not the rest of the circled-capital-letter alphabet.

Unlike with #16966, #14590 etc. no variation selector is involved here.

Further: trying to edit this text causes inconsistent rendering. The character width may appear corrected, only to move back when returning to normal mode. In some cases, a double glyph (not recognized as part of the text) appears until a redraw.

### Version of Vim

9.1.0016-1ubuntu7.18

### Environment

GNOME Terminal 3.52.0 (xterm-256color) on Linux Mint 22.3, Bash 5.2.21

I'm using the distro-packaged Vim, fully described:

```
VIM - Vi IMproved 9.1 (2024 Jan 02, compiled Jul 13 2026 17:17:48)
Included patches: 1-16, 647, 678, 697
Modified by [email protected]
Compiled by [email protected]
Huge version without GUI.  Features included (+) or not (-):
+acl               +file_in_path      +mouse_urxvt       -tag_any_white
+arabic            +find_in_path      +mouse_xterm       -tcl
+autocmd           +float             +multi_byte        +termguicolors
+autochdir         +folding           +multi_lang        +terminal
-autoservername    -footer            -mzscheme          +terminfo
-balloon_eval      +fork()            +netbeans_intg     +termresponse
+balloon_eval_term +gettext           +num64             +textobjects
-browse            -hangul_input      +packages          +textprop
++builtin_terms    +iconv             +path_extra        +timers
+byte_offset       +insert_expand     -perl              +title
+channel           +ipv6              +persistent_undo   -toolbar
+cindent           +job               +popupwin          +user_commands
-clientserver      +jumplist          +postscript        +vartabs
-clipboard         +keymap            +printer           +vertsplit
+cmdline_compl     +lambda            +profile           +vim9script
+cmdline_hist      +langmap           -python            +viminfo
+cmdline_info      +libcall           +python3           +virtualedit
+comments          +linebreak         +quickfix          +visual
+conceal           +lispindent        +reltime           +visualextra
+cryptv            +listcmds          +rightleft         +vreplace
+cscope            +localmap          -ruby              +wildignore
+cursorbind        -lua               +scrollbind        +wildmenu
+cursorshape       +menu              +signs             +windows
+dialog_con        +mksession         +smartindent       +writebackup
+diff              +modify_fname      +sodium            -X11
+digraphs          +mouse             -sound             +xattr
-dnd               -mouseshape        +spell             -xfontset
-ebcdic            +mouse_dec         +startuptime       -xim
+emacs_tags        +mouse_gpm         +statusline        -xpm
+eval              -mouse_jsbterm     -sun_workshop      -xsmp
+ex_extra          +mouse_netterm     +syntax            -xterm_clipboard
+extra_search      +mouse_sgr         +tag_binary        -xterm_save
-farsi             -mouse_sysmouse    -tag_old_static    
```

It's hard to imagine that Debian introduced the issue, but please let me know if I should contact them instead.

### Logs and stack traces

```shell

```

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