feat(grid): support highlighting duplicate and null values in column context menu

[lxk955]

Fixes #8794

Summary

• Adds column context menu actions under "Highlight" ("高亮") submenu to highlight duplicate values ("高亮重复值") and NULL values ("高亮空值"), with a "Clear Highlights" action and checkmark toggling.
• Supports both canvas grid and DOM/transpose views with distinctive colors:
  • Duplicates: amber background
  • NULLs: sky blue background
• Displays a highlighter icon indicator in the column header when highlighting is active on that column.
• Shows toast feedback with match counts when toggled on.
• Cleans up column highlight state automatically when new query results load.
• Added comprehensive unit tests for highlight computation, context menu integration, and header indicator rendering.
• Included multi-language translations across all 12 supported locales.

[t8y2]

Maintainer patch in 82c275c (on top of e3c1057) — the feature structure is solid (pure lib extraction, canvas/DOM/transpose parity, 12-locale i18n); this closes the two blocking review notes:

1. Perf: columnHighlightMatches now short-circuits to empty key sets when no highlight rules are active, before touching displayItems. Previously the computed eagerly materialized every RowItem (displayRowRefs.map(...)) on each edit/filter/load-more invalidation even with the feature unused — the canvas draw reads the key sets every frame. This follows the useDataGridSearch empty-query early-return precedent (#8524). The isNullValue wiring is factored into a shared columnHighlightMatchesFor helper.
2. Toast accuracy: the duplicate/NULL toast counts are now computed from the toggled columns' rules only. Previously the count spanned every active highlight column, so enabling duplicates on an all-unique column could toast another column's match count.

Deferred as a follow-up (wording choice, not patched): detection covers loaded rows only, so "No duplicate values found" can be premature on streamed results — consider "in loaded rows" phrasing later.

Checks run locally: vitest run dataGridColumnHighlight.spec.ts dataGridContextMenu.spec.ts — 21/21 passed; git diff --check clean.

[t8y2]

Thanks for the contribution! Merged in 79dca4b, will be released in the next version.