Summary

• Refactors the playground ShortcutsPlugin to use isExactShortcutMatch (from the core lexical package) instead of manual KeyboardEvent.code checks
• This fixes keyboard shortcuts being broken on non-QWERTY layouts (e.g., Dvorak), where physical key positions differ from the logical characters they produce
• The core library already fixed this in [lexical] Bug Fix: REDO_COMMAND not triggered with non-English keyboard layouts (Ctrl+Y / Ctrl+Shift+Z) #8155 by introducing isExactShortcutMatch, which uses event.key (logical character) instead of event.code (physical position), but the playground code was still using the old approach

The Problem

On Dvorak layout, pressing Ctrl+V (paste) would trigger the Superscript shortcut because the physical V key is at the position where . (Period) is on QWERTY. The ShortcutsPlugin was checking event.code === 'Period' which matches the physical key position regardless of layout.

The Fix

All shortcut matcher functions in shortcuts.ts now use isExactShortcutMatch(event, key, modifierMask) which:

1. Compares event.key (logical character) case-insensitively for standard keys
2. Falls back to event.code only for non-ASCII keyboard layouts (e.g., Russian) where event.key is non-ASCII
3. Correctly handles Dvorak and other remapped layouts by respecting the logical key

The heading shortcut handler in index.tsx was also updated to use event.key (which directly gives '1', '2', '3') instead of extracting the digit from event.code (e.g., 'Digit1').

Test plan

• All 103 unit test files pass (2706 tests)
• ESLint and Prettier checks pass
• Manual testing: On Dvorak layout, Ctrl+V should paste (not trigger Superscript)
• Manual testing: All playground shortcuts should work correctly on QWERTY layout
• Manual testing: Shortcuts should work on non-English keyboard layouts (e.g., Russian)

Fixes #8255