languages: Add syntax highlighting for HTML character references (#48629)

Brett Schneider created 

HTML character references like `·`, `'`, and `{` are
correctly parsed by tree-sitter as named nodes
(`html_character_reference` in TSX/JavaScript, `entity` in HTML), but no
highlight query captures them. This means they render as plain,
unhighlighted text in the editor.

This PR adds one-line highlight captures for each:

- **TSX** (`crates/languages/src/tsx/highlights.scm`):
`(html_character_reference) @string.special`
- **JavaScript** (`crates/languages/src/javascript/highlights.scm`):
`(html_character_reference) @string.special`
- **HTML** (`extensions/html/languages/html/highlights.scm`): `(entity)
@string.special`

`@string.special` is already styled by all built-in themes (One Dark,
Ayu, Gruvbox, etc.), so no theme changes are needed.

Release Notes:

- Added syntax highlighting for HTML character references (`·`,
`'`, `{`, etc.) in TSX, JavaScript, and HTML files.

Change summary

crates/languages/src/javascript/highlights.scm | 1 +
crates/languages/src/tsx/highlights.scm        | 1 +
extensions/html/languages/html/highlights.scm  | 1 +
3 files changed, 3 insertions(+)

Detailed changes

crates/languages/src/javascript/highlights.scm 🔗 

@@ -360,3 +360,4 @@
 (jsx_self_closing_element (["<" "/>"]) @punctuation.bracket.jsx)
 (jsx_attribute "=" @punctuation.delimiter.jsx)
 (jsx_text) @text.jsx
+(html_character_reference) @string.special

crates/languages/src/tsx/highlights.scm 🔗 

@@ -424,3 +424,4 @@
 (jsx_self_closing_element (["<" "/>"]) @punctuation.bracket.jsx)
 (jsx_attribute "=" @punctuation.delimiter.jsx)
 (jsx_text) @text.jsx
+(html_character_reference) @string.special