Use full bounds if fixed aspect ratio does not apply

If a non-resizable activity can fill the non-decor space,
its bounds should not exclude decor bounds because the
activity and decor can show as a continuous area. otherwise
unexpected letterbox may be created and IME cannot attach
to it due to the activity doesn't match parent's bounds.

Fix: 152197007
Test: SizeCompatTests#testAspectRatioMatchParentBoundsAndImeAttachable

Change-Id: I61d2c99702fb8642a3bf5728949489b6b98eb508