[Audiosharing] Refine share then pair flow

Currently when there is one active LEA headset and users toggle on the audio sharing, a dialog will pop up to ask users to pair new headset and share audio with it. After user click pair new device button on the dialog:

1. Route users to pair new device page.
2. If users pair an LEA headset, finish the pair new device page and
   auto add source to the headset with loading indicators on audio
   sharing page.
3. If users pair a classic headset, wait for timeout, pop up dialog
   saying the paired headset is not compatible for audio sharing and
   finish the pair new device page.

Test: atest
Flag: com.android.settingslib.flags.enable_le_audio_sharing
Bug: 331892035
Change-Id: Ifb9579db0ef57d3a379cb5d17c66a604d1396bb4