Allow IME to show when control target differs from DC target

cause:
In this particular case, IME is requested by editor in the window,
but before IME could be drawn, app shows a new popupWindow on top.
This popupWindow has FLAG_ALT_FOCUSABLE_IM but it also has transparency.
So, for legacy reasons it becomes the IME target in DisplayContent and
IME will not be shown as Dc target and window requesting IME don't match.

solution:
Allow window requesting IME to show IME if it is same as control target
and current DC target has transparency.

Fix: 155662459
Test: atest ImeInsetsSourceProviderTest

Change-Id: I3540f4f23c449c50baff9981b58c36afff302455