Refine FocusHandlingTest and InputMethodServiceDeviceTest

With CL[1], modified some test flows to ensure:

- Finishing editable window and back to previous editable window can
still receive onStartInput and commitText.

- After device screen off / on and unlick keyguard, it's still workable
for switching IME.

[1]: I1ef3d341af9d473d94d52fd1890deafbae2bc9e1

Bug: 160391516
Test: atest FocusHandlingTest
Test: atest InputMethodServiceLifecycleTest
Change-Id: Id48eedc1a2d5597bbba5f1d3fc01540e2f6de4c5
4 files changed