Fix overlay is expanded in split-screen

The overlay container will always be expanded when the host task is at the right side of
split screen. It's because the taskBounds use display space, while the
container bounds use relative bounds.

This CL uses relative taskBounds in #santizeBounds to fix the issue.

Test: atest OverlayPresentationTest
Test: manual - Launch the demo app to right side of split-screen and launch the overlay.
               It's expected to follow the configuration in demp app.
Fixes: 339611972
Flag: EXEMPT bugfix
Change-Id: I416bbbf18bcec9404fe230ebcae290821cb8d96f