AudioPolicy: Add unit tests for the MSD use cases

Test the following scenarios:
  - inputs / outputs update due to setForceUse change;
  - MSD device selection and downstream patch creation
    when an output for a supported format is opened;
  - default device selection and downstream patch teardown
    when an output for an unsupported format is opened;
  - swiching outputs depending on the format.

Bug: 121048134
Test: audiopolicy_tests
Change-Id: I3a07c758ea7fd87250f425c27fbf0c38eb5bf8b5