Allow hovering/pressing handle elements through status bar.

Extend the existing EventReceiver logic to also receive/process hover
and press events related to Desktop handle.

Since this adds hover processing to the collapse button which is only
partially in status bar, this CL also adds a custom ImageButton class
that does not handle hover events. This is to prevent a flicker from
happening when the hover moves from outside to inside the status bar
layer.

Bug: 316186265
Test: Manual
Change-Id: I6066b3ee9d1e5637f03f32e2e4b384e7a59e764e