Integration of LDAC Adaptive Bit Rate mechanism

LDAC ABR controls LDAC encoder bit rate based on A2DP transmit queue
length.
It can be used if the LDAC ABR library is installed on the device:
libldacBT_abr.so

Test: manual
Bug: 35381097
Change-Id: Idcc2fabe86acaf441f5a71f5d2bb66ad29252cdb