Add getMarkAsReadAction api, send Mark as read intent back to app

Once message has been played with TTS, FallbackAssistant should notify
messaging app that message has been read.

This change also refactors how TTS requests are tracked. Instead of sending
a listener to follow each TTS request, the TTS helper is instantiated with
one listener, and each request is tracked with its own unique ID.

Bug: 131421570
Test: Manual
Change-Id: I290fced826838ba8f99d9bf244d2df99aab3460d
3 files changed