Always report real top focused window to remote inset controller

When the focused window is not controlling the system bars but rather
it's the responsibility of a remote insets controller, the actually top
focused window should be passed rather than limiting to a fullscreen
window only.

Bug: 440148796
Test: atest InsetsPolicyTest
Flag: NONE bugfix
Change-Id: I9ff3483f2d9c6a7f17798567a1a3c88dfadfb29b