Fix ST recognition requested after start error

When recognition does not succeed due to contention, device state, or
another unexpected error, the STService session is left in a requested
state, which can resume recognition later unbeknownst to the client.

Return success and send an immediate pause if the service will handle
resuming. Otherwise, set the state to be not requested.

Fixes: 268218045
Test: new AlwaysOnHotwordDetectorTest methods
Test: Manual verification with EBS for AGSA/now playing
Change-Id: I01c6a49a859bde9cd6574d0df9325f6fa7b0b685