Add test to for disposing status bar input layer if caption is below status bar

When an app transitions from fullscreen to split, the status bar input
layer is was not being disposed, so it sometimes intercepts the motion
events of the top caption bar when tasks are in vertical split. This was
fixed in Ib555ca568e2941e3cbed2cada2a64803bfcfb0ac and this change adds
a test for that change.

Bug: 380208494
Test: attempt to interact with caption when in vertical split
Flag: com.android.window.flags.enable_desktop_windowing_mode
Change-Id: Ib555ca568e2941e3cbed2cada2a64803bfcfb0ac