setBoundsChangeTransaction: Fix two issues

1. Ensure it only applies to the root of the task. This
is to ensure we don't get tricked in to thinking the app
is resizing when the PIP menu resizes. As a next step we
still need to keep the PIP menu from resizing.
2. Also defer the Transaction on the Task SurfaceControl
not just the Window itself. This was just a typo in
the original implementation.

Bug: 150810705
Test: Change PIP size. Main window is flicker free.
Change-Id: I26d82b5f73110aaa8fe730edfd07c87e7cf84c0d