Pipe windowToken of window requesting IME

It takes time from when IME is requested to the time when IME is ready
to be shown. When its ready to be shown, we need to make sure that
window that requested IME is still the IME target in DisplayContent. The
only realistic way of knowing originating window is passing windowToken
from IMM API.

Bug: 111084606
Test: CtsInputMethodTestCases

Change-Id: Ia49e23dd077d264a58d28a7b8acffde54b7db187