[Audiosharing] Reimpl audio sharing main switch

New flow: Automatically add sharing source to connected active device eligible for
audio sharing. And then pop up the dialog for users to choose an additinal eligible device
to share audio.

Old flow: Pop up the dialog first and add sharing source after user
interact to the dialog.

Flagged with enable_le_audio_sharing

Bug: 305620450
Test: Manual
Change-Id: If0d1609b2677ca9ecae926c198f305fd1f4e34d3