Handle ble_scanner scan_results in main thread

Scan results from GD should be handled in the main thread to avoid
synchronization issues when accessing common resources.

Change-Id: Id4b6d94cd36e8f68a93d6903c4381c5b2a7ad619
Test: mmm packages/modules/Bluetooth
Flag: com.android.bluetooth.flags.scan_results_in_main_thread
Bug: 387997483
Bug: 392693506