Replace region intersection change from quickReject to use Region#op

quickReject only checks outer bounds and not the invididual region
boundaries, this might give false negative (as the method doc suggests).

This caused a bug where window is still added to a11y window list
although it has been fully covered by a dialog (still intersects with
unaccountedSpace).

Bug: 240885392
Test: atest android.autofillservice.cts.servicebehavior.SettingsIntentTest
Change-Id: I7fc226e2288c2433e427d1e8ef173a3a21a20edc