Store pointers per-device

Previously, input dispatcher assumed that a single input device is
active. However, we are trying to add multi-device support.

In this CL, store the pointers inside touched windows on a per-device
basis. This CL should not cause any behaviour changes. We expect there
to be a single device active at a time still.

Bug: 211379801
Bug: 281806933
Test: m inputflinger_tests && $ANDROID_HOST_OUT/nativetest64/inputflinger_tests/inputflinger_tests
Change-Id: I73fc4adcf306bb49e153f3daeed68753e0632c86
Signed-off-by: Siarhei Vishniakou <svv@google.com>