Please expose class hierarchy/class list/filtering code from SClassViewer.cpp

There is so much code hidden away in SClassViewer.cpp that could be reused. I’ve lost count of the number of times I’ve wanted this stuff for editor plugins, in particular being able to generate and filter a list of all classes, including unloaded blueprints. I’m fairly sure I’ve even seen other places in the engine that need it and have instead duplicated a simpler version locally.

Please!