Allow multiple input device in the same window

With this change, all restrictions about only having a single input
device active in a window are lifted.

The window will get multiple input devices at once.

21 native tests were forked in this CL to reflect the new behaviour.

Bug: 211379801
Test: navigate settings with touch + stylus at the same time
Test: swipe inside IME with touch + stylus
Test: draw in test app with touch + stylus
Test: TEST=inputflinger_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
Change-Id: I259c0c87e47a1fa3090cddba6a595cf032877bb2