fix(autocomplete-preset-algolia): support Unicode in ReverseHighlight

[rinoshiyo]

Summary

This PR fixes ReverseHighlight behavior for non-ASCII queries (e.g., Japanese and Cyrillic) in @algolia/autocomplete-preset-algolia.

isPartHighlighted previously used an ASCII-only \w check to detect "word characters". In JavaScript, \w matches [A-Za-z0-9_] and does not match Unicode letters. As a result, Unicode text could be treated as a "separator" by the normalization logic, which could lead to incorrect ReverseHighlight output (see #1317).

This change replaces the ASCII-only check with a Unicode-aware check (Unicode property escapes) and renames the variable accordingly. A fallback to the previous \w behavior is kept for environments where Unicode property escapes are unavailable.

Result

npm test -- --testPathPattern=isPartHighlighted\.test\.ts

Output:

 PASS  packages/autocomplete-preset-algolia/src/highlight/__tests__/isPartHighlighted.test.ts
  isPartHighlighted
    ✓ returns the isHighlighted value with a missing sibling (1 ms)
    ✓ returns the isHighlighted value with both siblings (1 ms)
    ✓ does not treat Japanese text as a separator at the start (俺はジャイアン)
    ✓ does not treat Japanese text as a separator in the middle (俺はジャイアンだ)
    ✓ does not treat Japanese text as a separator at the end (俺はジャイアンだ)
    ✓ does not treat Cyrillic text as a separator at the start (regression #1317)
    ✓ does not treat Cyrillic text as a separator in the middle (regression #1317)
    ✓ does not treat Cyrillic text as a separator at the end (regression #1317)

Test Suites: 1 passed, 1 total
Tests:       8 passed, 8 total
Snapshots:   0 total
Time:        0.493 s, estimated 1 s

fixes #1317

UI Evidence (Before / After)

Before (current behavior)

• Query: 音声
• ReverseHighlight does not highlight the non-matching suffix part as expected.

After (this PR)

• Query: 音声
• ReverseHighlight highlights the non-matching suffix (e.g., "dl book") while keeping the matching prefix unhighlighted.

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Sandbox	Source
@algolia/autocomplete-example-github-repositories-custom-plugin	Configuration
@algolia/autocomplete-example-instantsearch	Configuration
@algolia/autocomplete-example-playground	Configuration
@algolia/autocomplete-example-preview-panel-in-modal	Configuration
@algolia/autocomplete-example-starter-algolia	Configuration
@algolia/autocomplete-example-starter	Configuration
@algolia/autocomplete-example-reshape	Configuration
@algolia/autocomplete-example-vue	Configuration

[Haroenv]

thanks, this looks great, and still safe for older browsers

[Haroenv]

moved to #1331 so that CI can run