[OutputSwitcher] Support release system session (P1)

1. add getReleaseType to indicate if the session supports releasing and
   how to release it
2. bridge releaseSession between output switcher and SystemMR2Provider

Next step: Impl getReleaseType and releaseSession in SystemMR2Provider

Test: atest
Bug: 385672684
Flag: com.android.media.flags.enable_output_switcher_personal_audio_sharing
Change-Id: I573301c781757065af7f8208e88b085a78df93f3