fix(window magnification): Update the boundary for window magnifier at the bottom

To avoid gesture conflicts between the window magnifier and system
gestures at the bottom of the screen, we don't allow the window magnifer
to overlap with the system gesture botton inset.

Bug: 380320995
Test: atest WindowMagnificationControllerTest
Flag: com.android.systemui.update_window_magnifier_bottom_boundary
Change-Id: I11a56f586ffdedf63f6321f9ba01e8e71e4fe7a5