Disable the PiP dismiss target if input is not touch screen.

This is a product behaviour change as the dismiss target might not be
intuitive for non-touch inputs (see linked bug).

Flag: com.android.window.flags.enable_dragging_pip_across_displays
Fixes: 414604420
Test: atest PipTouchHandlerTest
Change-Id: Ic39275ecae949e704c990c0dfc47887014cf9b07