Adds support to the new information offered by KWin. Now it can tell us
that the current client doesn't support Wayland input methods.

Therefore, it sets the plasmoid in a new "unsupported" state that will
offer to force an activation when triggered. KWin will then be able to
emulate a keyboard and it all should work to some extent.

Depends on kwin!2907

BUG: 439911