Fixes #28237: Identify keyboard layouts where A-Z are missing or unusual and assume the standard mapping for KeyA - KeyZ

- language
- resource

TS 2.3.1 introduced a breaking change by [switching to covariant types for callbacks](https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#covariance-in-callback-parameters). This change tries to fix these compiler errors in the workbench codebase

- Implement APIs in ResolvedKeybinding to expose parts
- Implement APIs in ResolvedKeybinding to get labels without modifiers
- Adopt tests to above API changes
- Use above APIs to search and highlight keybindings
- A new keybinding label widget to render a keybinding
- Adopt above widget in Keyboard shortcuts editor and define keybinding widget