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/device_enumerator.cpp

@@ -190,6 +190,8 @@ DeviceEnumerator::~DeviceEnumerator()
  * with a warning message logged, without returning an error. Only errors that
  * prevent enumeration altogether shall be fatal.
  *
+ * \context This function is \threadbound.
+ *
  * \return 0 on success or a negative error code otherwise
  */