rdp: validate button state

Discard and log duplicate release or press events. Log and discard
invalid button ids.

This prevents buggy clients from causing problems in weston's internal
state - like breaking idle inhibition button counting.

Co-authored-by: Steve Pronovost <spronovo@microsoft.com>
Co-authored-by: Brenton DeGeer <brdegeer@microsoft.com>
Signed-off-by: Hideyuki Nagase <hideyukn@microsoft.com>
Signed-off-by: Steve Pronovost <spronovo@microsoft.com>
Signed-off-by: Brenton DeGeer <brdegeer@microsoft.com>