Add support for keyboard shortcuts panel on TV

The keyboard shortcuts panel lists available shortcuts for the currently
focused app + system shortcuts.
Apps can request the panel to be shown by calling
Activity#requestShowKeyboardShortcuts.

Calling this method on TV caused SystemUI to crash, as
KeyboardShortcutsReceiver couldn't be instantiated.
Adding the KeyboardShortcutsModule on TV fixes this crash.

Adding the override for toggleKeyboardShortcutsMenu in TvStatusBar
enables the global toggle shortcuts panel shortcut to work.

The other changes are to improve usability of the dialog on TV:
- Make the list rows focusable
- Give the whole row a suitable contentDescription for a11y
- Give the items a background that highlights the focused row
- Hide the "Recents" row on devices that do not support it (like TV)

Bug: 278514212
Test: manual on TV device
Change-Id: Ia8285d5b05ad909cecb16eb087cbbc56ed86475a