Multi-A2DP: Fix timing and codec measurement in metrics

* Copy BtifMediaStats and SchedulingStats when updating metrics
  to avoid race conditions
* Do not log audio_duration_ms if session_end_us <= session_start_us
* Clear cached A2DP metrics when LogBluetoothSessionEnd() is called
* Log codec information along-side A2DP metrics
* Log whether A2DP offload is enabled along-side A2DP metrics

Multi-A2DP:
* Log LogBluetoothSessionStart at btif_a2dp_source_start_session_delayed
* Log LogBluetoothSessionEnd at btif_a2dp_source_end_session_delayed

Unit Test:
* Wrote A2DPSessionTwoUpdatesSeparatedbyEndTest that will fail if A2DP
  metrics are not cleared when LogBluetoothSessionEnd is called

Bug: 109953464
Test: make, net_test_osi::BluetoothMetricsLoggerTest,
      net_test_osi::BluetoothA2DPSessionMetricsTest
Change-Id: I6a311dce8035ce2e3f39773c260ea9eaef73e45b