bluetooth.audio@2.1: add handle IsSessionReady for LE offload encoder

Bug: 150670922
Tag: #feature
Test: vts-tradefed run vts -m VtsHalBluetoothAudioV2_1TargetTest
Change-Id: I5d5ca0cb63b2801b3ad1351754ebd9f5da73ac1e
3 files changed