Camera: VTS: Wait for release fence before consuming buffers

The camera HAL may signal release fence after processCaptureResult.
If the VTS test waits for the release fence in the context of the
capture result, there is possibility of deadlock.

Rather, we should wait for the releaseFence in a different thread
context to really emulate the real application behavior.

Test: atest VtsAidlHalCameraProvider_TargetTest
Bug: 241281568
Change-Id: Id1d92e901aae1cab084846d252ef090fcda182d7