Splitting VoiceRecognitionHandlerTest into 3 separate tests.

VoiceRecognitionHandlerTest was the third biggest and it could take up
 to 10 mins to run it. In order to reduce time needed to investigate
flakines or any test issues, it is now split into 3:
- VoiceRecognitionHandlerTest: tests basic flow and mechanisms shared
between system and assistant recognition
- AssistantVoiceRecognitionHandler: tests the preconditions and voice
 recognition done by the Assistant
- AssistantActionsHandlerTest - tests of the additional Assistant
features: actions

Bug: 1258161
Change-Id: I75b2513b3644ddeaad9c8e56cb7735f7f6240503
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3832071


Reviewed-by: Josh Simmons <jds@google.com>
Commit-Queue: Basia Zimirska <basiaz@google.com>
Cr-Commit-Position: refs/heads/main@{#1044785}