base

Fix reference cycle in InputEventReceiver and Sender.

If the receiver or sender was not properly disposed, then
the underlying input channel might be leaked because the
native peer was holding a strong reference to the object.

Switched to using a weak reference.

Also updated Binder to use a new helper created for this purpose.

Change-Id: I19680bf96d0548777bff02aa1d91874d1e8e41da