The color resources starting with `@android:color/system_` are not
available on API < 31.

No effort is made to implement the Monet feature on Android 9. Instead,
the monet themes look like the Dark and Light themes.

This adds the clipboard pane, which allows to save an arbitrary number of
clipboards and to paste them later. The key can be disabled in settings.

Checking the "Recently copied text" checkbox will cause the keyboard to keep a
temporary history of copied text. This history can only contain 3 elements
which expire after 5 minutes.
If this is unchecked, no history is collected.

History entries can be pinned into the persisted list of pins.

Keys that are not in the pending compose sequence are greyed out with
the new 'FLAG_GREYED' flag.