libcamera: Document thread-safety attributes of core classes

Define the thread-safety attributes of the classes and methods that are
either thread-safe or thread-bound. The CameraManager, Camera and
PipelineHandler will be addressed separately.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/thread.cpp

@@ -222,6 +222,8 @@ ThreadData *ThreadData::current()
  * called. A custom event dispatcher may be installed with
  * setEventDispatcher(), otherwise a poll-based event dispatcher is used. This
  * behaviour can be overriden by overloading the run() method.
+ *
+ * \context This class is \threadsafe.
  */
 
 /**