Add locks to InputDispatcher_test

The variables inside the policy are being called from the test thread
and the InputDispatcher thread. They are being accessed without a lock
today. This is OK because we are waiting for dispatcher to go to idle
today, but in ag/10847700 we will have dispatcher not idle, and need to
have a way to wait for a policy callback from the test thread with a
certain timeout.

Add locks to the policy variables here to reduce the diff.

Bug: 143459140
Test: atest inputflinger_tests
Change-Id: I77f5ec15cdfd55ce4c4dfcb501071b2c7c961b1b