Split telemetry for MediaSession (voice command) rewind/fast-forward

[mcomella]

Why/User Benefit/User Problem

Rewind and fast-forward MediaSession commands both go to a "seek" command using an absolute position: as such, we cannot easily distinguish them. With #943, I opted to add the simple telemetry to tell us if a seek command has been issued. However, we can calculate whether the command was a "fast-forward", "rewind", or even (more easily) "rewind to the beginning" based on the current playback time. This give us additional insight into how users use Fire TV for videos.

Note that we'd have to do these calculations from Java -> JS -> Java, which is why it's non-trivial (or maybe we can use MediaController.getPlaybackState().getPosition() all in Java, which is mostly accurate?

What / Requirements

• Decide which probes we'd measure
• Add probe

Acceptance Criteria (how do I know when I’m done?)

[mcomella]

If we wanted to answer questions with this telemetry, we'll file a new bug for it.