libcamera: ipa_manager: Remove singleton requirement

The IPAManager class implements a singleton pattern due to the need of
accessing the instance in a static member function. The function now
takes a pointer to a PipelineHandler, which we can use to access the
CameraManager, and from there, the IPAManager.

Add accessors to the internal API to expose the CameraManager from the
PipelineHandler, and the IPAManager from the CameraManager. This
requires allocating the IPAManager dynamically to avoid a loop in
includes. Use those accessors to replace the IPAManager singleton.

Update the IPA interface unit test to instantiate a CameraManager
instead of an IPAManager and ProcessManager, to reflect the new way that
the IPAManager is accessed.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/pipeline_handler.cpp

@@ -719,6 +719,13 @@ void PipelineHandler::disconnect()
  * \return The pipeline handler name
  */
 
+/**
+ * \fn PipelineHandler::cameraManager() const
+ * \brief Retrieve the CameraManager that this pipeline handler belongs to
+ * \context This function is \threadsafe.
+ * \return The CameraManager for this pipeline handler
+ */
+
 /**
  * \class PipelineHandlerFactoryBase
  * \brief Base class for pipeline handler factories