Shift RoundedCornerOverlay to Display window hierarchy

ScreenDecorations use rounded corner overlay flag and are
currently drawn outside of the window hierarchy,
It currently blocking touches to the gesture monitor spy
windows. By bringing them to Display content Surface control,
we make them in the same tree as the gesture monitor. And
since gesture monitor window are hugher in z ordering they
will take precedence for touch events over ScreenDecorations.

Test: manual

Bug: 225505986
Change-Id: If60450c5e6f29c23a96ce8a89a5ba7d47ee8609d