Support AVRCP Controller on JNI thread

Recent changes to threading of the BTA layer require that all JNI
callbacks are performed on the JNI thread.  This change updates the APIs
to ensure that the data passed is thread safe.

Bug: 79145011
Test: Browse and Play music via AVRCP Controller.
Change-Id: I191658ea90c96bcf372e772119db6c31c9010230