Add test for HOVER_EXIT when another device is touched

When there's currently a hovering pointer, it should be canceled via
"HOVER_EXIT" whenever another device touches down (by sending
ACTION_DOWN).

Bug: 268683979
Test: m inputflinger_tests && $ANDROID_HOST_OUT/nativetest64/inputflinger_tests/inputflinger_tests
Change-Id: Ib839c8d6c1f949a5c7f62739b989aa9ec7481058