This makes it easier to spot syntax errors when editing the
class reference. The schema is referenced locally so validation
can still work offline.
Each class XML's schema conformance is also checked on GitHub Actions.
-Allows displaying custom options for specific file format variants
-Added support for scene format import to retrieve custom options
This PR is necessary for #54886 to be implemented properly.
* New plugin system to control the whole import workflow
* Can add options and run code at every import step (general, per node, mesh, animation, material etc.)
This constitutes a first version of these plugins. The ability to interact with the import preview dialog will likely be added later on.