[Android] implement MediaSession::onMediaButtonEvent

[peak3d]

Description

This replaces the logic of translating MediaSession events to keypresses introduced here:
#15654

Android provides the possibility to override the MediaKey keypresses before they are handled in MediaSession. This is required to get up / down state and timings between these two states.

Motivation and Context

Issues reported here: #15003

How Has This Been Tested?

• Play a movie
• Press a MediaKey on remote (e.g.fast forward / rewind).

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)