Observe frame info from native input code

Before this CL, the java-based FrameObserver was created in ViewRootImpl
and acted as a proxy between HardwareRenderer and
NativeInputEventReceiver. This caused occasional jank due to garbage
collection, because java objects would be created as part of that
pipeline.

More specifically:
1. The observers are notified from native code
2. The observer is implemented in ViewRootImpl. It's a jni call in order
   to process the observer's notification.
3. The observer processed the frame stats (input event id, gpu completed
   time, and present time) and passed it to NativeInputEventReceiver,
   which is also in native code.
So the path used to be: native -> jni -> java (viewRootImpl) -> jni ->
native.

In this CL, the pipeline is rewired such that the native code is talking
directly to native code, without java. Java is only used in order to
register the observer.

Now, InputEventReceiver creates a FrameMetricsObserver directly in the
native code. This observer is then registered through java with
HardwareRenderer. The notifications about frame stats are now processed
directly in native input code.

Bug: 376713684
Test: statsd_testdrive 375 (after overriding SLOW_EVENT_MIN_REPORTING_*
constants to 0 locally to force it to report all events).
Test: atest InputEventSenderAndReceiverTest
Flag: EXEMPT refactor

Change-Id: I1aa7df730749c78062398632c3a9abb443507bef