Shortcut Helper - Filter shortcut commands containing unsupported keys

Different keyboards have different keys, and some might not have the
keys specified by a shortcut command.

+ Refactors the repository to process all shortcut group sources as one
  list

Test: ShortcutHelperCategoriesRepositoryTest
Flag: com.android.systemui.keyboard_shortcut_helper_rewrite
Fixes: 353894416
Change-Id: I4af5b80f64d36dd40095a287a032629b9a70c82a