Make sure to call back reportFinish() on the desired Handler.

Before exposing #reportFinish() as a public API, we have to fix an
existing bug that my previous CL [1] for Bug 26945674 forgot to take care.

Currently BaseInputConnection#reportFinish() is always called by using
the root view's Handler.  We should move the logic to call
BaseInputConnection#reportFinishInputConnection() from ViewRootImpl to
IInputConnectionWrapper to make sure that the method in question can
always be called on the desired Handler.

To make things simple, instead of explicitly calling #reportFinish()
from IMM, this CL let ControlledInputConnectionWrapper#diactivate()
internally call #reportFinish() as needed.  This makes it easier to make
sure that #reportFinish() is called after all the queued method calls
are handled.

  [1]: Id9e579bb3e2966986cdcb1c34bc8cacfeca2e1a9
       612cce92

Bug: 25332806
Change-Id: Ibe94f115e607a198d12ecd3d4e4f91a7d9469c98