Fix fullscreen task bounds assumption

On some android devices, the task bounds may not be fullscreen
by default. This CL fixes the assumption by using #getTaskBounds
instead of #getTaskWidth/Height

Test: atest cts/tests/framework/base/windowmanager/jetpack/src/android/server/wm/jetpack/embedding
Bug: 311123689

Change-Id: I49a9562a621d117c852555163ddbc3a5ec7246fc
5 files changed