Move BT framework test utils to test_utils package

* Leaving an alias in android.bluetooth.cts so that dependencies can
  still compile

MUST_SLEEP=Legacy CTS code still use Thread.sleep(). Hence this library
cannot avoid it.

Bug: 300052980
Test: atest CtsBluetoothTestCases
Test: atest CtsRootBluetoothTestCases
Change-Id: I14f5f334144834710f14616301ae8b5e4df9068d