Replace gear button with "+" button for audio sharing available devices, and...

Replace gear button with "+" button for audio sharing available devices, and check mark for devices in audio sharing session.

For this CL, clicking on them still go to settings. Behavior change will be in the next CL.

Test: atest
Bug: 382397280
Flag: com.android.settingslib.flags.enable_le_audio_sharing
Change-Id: Iebc43ad26513087381730ba6b92e862068958f14