Use sequence numbers to synchronize enabling Pointer Capture (1/2)

InputReader only processes configuration change from its main thread.
This means that if there is more than one Pointer Capture change
request when the thread is busy or sleeping, it will only process the
latest one. To ensure requests to enable Pointer Capture are synchronized
with Dispatcher, we must use sequence numbers.

Requests to enable Pointer Capture have a sequence number. Requests to
disable Pointer Capture do not have a value.

Bug: 195312888
Test: atest inputflinger_tests
Test: manual with GeforceNow app, see bug.
Merged-In: I6ae9c5498dc2f783b4c7211fa3665d42e29d2919
Change-Id: I6ae9c5498dc2f783b4c7211fa3665d42e29d2919