[WIP] [Keyboard Manager] Add exact match and orphaned-key notice to the new editor

[moooyo]

Summary of the Pull Request

Closes two functional-regression gaps in the new WinUI 3 Keyboard Manager editor (KeyboardManagerEditorUI, the default editor when useNewEditor is on) relative to the classic C++ XAML-Islands editor:

• Exact Match for shortcuts — the per-origin-shortcut "exact match" flag (already supported and serialized by the engine, but never wired into the new editor).
• Orphaned-key notice — a heads-up when a single-key remap leaves the original key with no way to be typed, mirroring the classic Remap Keys editor (reworked as a non-blocking notice to fit the new per-mapping flow).

⚠️ WIP / Draft — opened for early review. Not yet discussed with core contributors; no automated tests added (the new editor has no unit-test project yet). Validated via build + manual round-trip + code review.

PR Checklist

• Closes: #xxx
• Communication: I've discussed this with core contributors already. If the work hasn't been agreed, this work might be rejected
• Tests: Added/updated and all pass
• Localization: All end-user-facing strings can be localized
• Dev docs: Added/updated
• New binaries: N/A — no new binaries; only existing Keyboard Manager projects changed

Detailed Description of the Pull Request / Additional comments

1. Exact Match

Shortcut::exactMatch already exists in the engine and is (de)serialized by MappingConfiguration for every shortcut remap type, but the new editor never exposed or persisted it. This PR threads it end-to-end:

• Native wrapper (KeyboardManagerEditorLibraryWrapper): new exactMatch on the ShortcutMapping struct and the AddShortcutRemap export; GetShortcutRemap / GetShortcutRemapByType populate it from the origin shortcut.
• Interop / service (KeyboardManagerInterop, ShortcutKeyMapping, KeyboardMappingService): marshal the flag both ways (int across the P/Invoke boundary, bool in managed code).
• UI (UnifiedMappingControl, MainPage): an ExactMatchCheckBox (enabled only for multi-key shortcuts), wired through all action types (key/shortcut, text, URL, program, disable) on save, load and edit — matching the classic editor, which gates exact-match on the origin shortcut regardless of target type.

2. Orphaned-key notice

Wires up the previously-unused ValidationHelper.IsKeyOrphaned to inform the user when a single-key remap leaves the original key unreachable. Because the new editor saves one mapping at a time (unlike the classic batch editor), this is surfaced as a non-blocking, dismissible InfoBar shown after saving — saving still completes in a single click — rather than a modal confirmation.

Commits

• b7556c8 Add exact match and orphaned-key warning to the new WinUI3 editor
• 3197ae1 Fix issues found in review (exactMatch dropped on multi-key text re-enable; checkbox enable-state not synced on dropdown edits; IsKeyOrphaned now only counts key-output remaps as restoring a key)
• ab99b6f Make the orphaned-key warning a non-blocking notice

Validation Steps Performed

• Build: KeyboardManagerEditorLibraryWrapper (native) and KeyboardManagerEditorUI (C#) both build clean at x64 Debug (exit code 0).
• Persistence: verified in code that the engine serializes/loads exactMatch for shortcut→key/shortcut/program/URI/text, so the flag round-trips to both the engine default.json and the editor's editorSettings.json.
• Review: independent code-review and rubber-duck passes; the issues they surfaced are fixed in 3197ae1 (see commits).
• Manual: exercised save/load/edit of exact-match shortcuts and the orphaned-key notice.

Still TODO before ready-for-review: agree the change with core contributors, and add automated coverage once/if a test project exists for the new editor.