enh(markdown) add entity support

[dschach]

Changes

Replicated changes suggested by TaraLei in #3911 and updated to latest markdown specs https://github.com/highlightjs/highlight.js/pull/3911

• Add ENTITY regex for markdown.
• Latest markdown specs are https://spec.commonmark.org/0.31.2/#entity-references (1/28/2024)

Included changes updates

Checklist

• [x] Added markup tests, or they don't apply here because...
• [x] Updated the changelog at CHANGES.md

Note: Please squash because extra commit details are here due to unrelated work on my fork

[github-actions[bot]]

Build Size Report

Changes to minified artifacts in /build, after gzip compression.

5 files changed

Total change +112 B

View Changes

| file | base | pr | diff | | --- | --- | --- | --- | | es/core.min.js | 8.17 KB | 8.17 KB | +1 B | | es/highlight.min.js | 8.17 KB | 8.17 KB | +1 B | | es/languages/markdown.min.js | 905 B | 960 B | +55 B | | highlight.min.js | 8.21 KB | 8.21 KB | +1 B | | languages/markdown.min.js | 906 B | 960 B | +54 B |