* Refactor interface to PdmObjectHandle and PdmFieldHandle
Return objects instead of passing in structures as parameters
* Add nodiscard to several functions
* Remove redundant this->
* Rename to ptrReferencedObjectsByType
fieldChanged() can potentially do much work. When toggling objects in the project tree, make sure that fieldChanged is called only once for a toggle operation. This will make sure that we have the best possible performance in all use cases.