Race condition in QtCamera2.java

There is a race condition in the QtCamera2.java several members such as mState and mCaptureSession. This is accessed from the background thread that handles state and capture-callbacks. It is also accessed from the "takePhoto()" method which is called from C++ on whatever thread the QCamera lives within.

Currently this issue is not actively causing misbehavior and fixing it would require significant effort and testing to make sure we don't introduce regressions and new bugs. Until we have customer bugreports related to this, we don't have to fix this immediately.