Camera: Release extension resources after closing handler thread

To avoid possible concurrency issues, always quit the handler
thread before releasing any extension resources.
In case camera is still running, camera callbacks can still
be handled during release which can result in concurrency
exceptions.

Bug: 195595369
Test: atest -c
cts/tests/camera/src/android/hardware/camera2/cts/CameraExtensionSessionTest.java

Change-Id: I473a4cb04e5ea27b5c8f8221a2390219a7915e73