audio policy: fix capture policy for assistant

Fix concurrent capture policy for assistant: allow assistant to capture if
running as foreground service too and not only if on top.

Same fix for accessibility service.
Also refine logic for single active client on top by retaining the
latest started capture from an app on top (in case several apps can be on top).
Also fix priority between app on top and app with foreground service.

Bug: 120588242
Bug: 111438757
Test: Manual capture tests with solotester and Camera, Assistant and Duo
Test: CTS tests for AudioReco
Change-Id: I2fc54853a584b9e9e48c012b0c3a2bcc8436a340