`KeyBinding` elements currently always render their shortcut labels.
Applications with a touch-oriented interface cannot remove those
keyboard-only visual affordances without changing each consumer or
unregistering the shortcuts themselves.

This adds an application-wide visibility policy to the reusable
`KeyBinding` component, so context menus and other consumers follow the
same setting. Registered keybindings and `aria-keyshortcuts` remain
intact, and labels remain visible by default.

## Testing

- `cargo nextest run -p ui --lib`
- `cargo fmt --check`
- The final unused-override cleanup was not rerun because `nix develop`
currently fails while building the existing `zed-editor-deps`
derivation: `corgi-patches/scratch/Cargo.toml` is absent from its Nix
source.

Release Notes:

- N/A