Unify the LE audio string and refine the layout to put LE audio switch together

Screenshot: https://screenshot.googleplex.com/A6PwLhscRUypgYK

Bug: 233018305
Bug: 233005340
Test: make RunSettingsRoboTests ROBOTEST_FILTER=BluetoothLeAudioPreferenceControllerTest
Test: switch LE audio feature, and check LE audio functionality status
Change-Id: I2d650eb315790c3efc7510d9e125aeaf4464cda6