This PR refactors the highlight map capture name resolution to be faster and more predictable. Speficically,

• it changes the capture name matching to explicit prefix matching (e.g., function.call.whatever.jsx will now be matched by only function, function.call, function.call.whatever and function.call.whatever.jsx). This matches the behavior VSCode has
• resolving highlights is now much more efficient, as we now look up captures in a BTreeMap as opposed to searching in a Vector for these.

This substantially improves the performance for resolving capture names against themes. With the benchmark added here for creating the HighlightMap, we see quite some improvements:

Running benches/highlight_map.rs (target/release/deps/highlight_map-f99da68650aac85b)
HighlightMap::new/small_captures/small_theme
                        time:   [161.90 ns 162.70 ns 163.55 ns]
                        change: [-39.027% -38.352% -37.742%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 3 outliers among 100 measurements (3.00%)
  3 (3.00%) high mild
HighlightMap::new/small_captures/large_theme
                        time:   [231.37 ns 233.02 ns 234.70 ns]
                        change: [-91.570% -91.516% -91.464%] (p = 0.00 < 0.05)
                        Performance has improved.
HighlightMap::new/large_captures/small_theme
                        time:   [991.82 ns 994.94 ns 998.50 ns]
                        change: [-50.670% -50.443% -50.220%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 5 outliers among 100 measurements (5.00%)
  5 (5.00%) high mild
HighlightMap::new/large_captures/large_theme
                        time:   [1.6528 µs 1.6650 µs 1.6784 µs]
                        change: [-91.684% -91.637% -91.593%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) low mild

For large themes and many capture names, the revised approach is much faster.

With that in place, we can also add better fallbacks whenever we change tokens, since e.g. a change from @variable to @preproc would previously cause tokens to not be highlighted at all, whereas now we can add fallbacks for such cases more efficiently. I'll add this later on to this PR.

Self-Review Checklist

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Release Notes:

• Improved resolution speed of theme highlight capture names. This might change highlighting in some rare edge cases, but should overall make highlighting more predicatable. Theme captures will now follow a strict prefix matching, so e.g. function.call.decorator.jsxwill now be matched by onlyfunction, function.call, function.call.decoratorandfunction.call.decorator.jsx` with the most specific capture always taking precedence.