Reduce dropped event logging in dispatcher

These logs were guarded with DEBUG_FOCUS until the guard was removed in
this CL:
21431224: Allow new gestures to cancel current gestures

Unfortunately, there's not a good way to reduce these logs. We should
already be logging the decision to drop the initial events like
ACTION_DOWN and ACTION_POINTER_DOWN. So the fact that we are dropping
ACTION_MOVE and others may not be that interesting.

These logs are currently causing people to incorrectly triage bugs to
the input team.

In this CL, make these logs dynamic so that they are only turned on when
needed.

Bug: 245989146
Test: TEST=inputflinger_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
Change-Id: I7510fa56d163da1e635b00f4025b3bf2c00ade6e