switcherPopup: Add support for modifier-less keybinding navigation
This drops the requirement that SwitcherPopups need a modifier based
keybinding to work.
The existing behavior for modifier based keybindings is kept but if
the popup is triggered from a no modifiers keybinding, instead of
finishing when the modifier is released, we use a timer that
automatically finishes the popup. The timer is reset on every key
release to allow navigation to happen.