[Audiosharing] Change main toggle enable conditions.

Enable the toggle when:
1. In audio sharing
2. No connected LEA device. We will show dialog to guide users to
   connect a compatible device.
3. Has active device, which means it is a healthy state after broadcast
   -> unicast switch.

Flag: com.android.settingslib.flags.enable_le_audio_sharing
Test: atest
Bug: 305620450
Change-Id: I2c8067f7882df6943beb3704f63a3e1113ce55d2