a2dp: Expose all supported codecs through BluetoothA2dp#getSupportedCodecTypes

this change adds the offloaded codec to the list of returned codecs;
previously the list was populated only with know codecs (SBC, AAC, AptX..)

Bug: 308686081
Bug: 305734815
Test: atest BluetoothA2dpTest#getSupportedCodecTypes
Test: m com.android.btservices
Change-Id: Iaab0a01964e1c5892a24e8abda07f7caf2dcc13a