Add structs

[thomascswalker]

I created a simple method to generate all the stubs for all StructDef objects. I've got a pretty vanilla install of Max 2023 so it should be free of third party plugins. Wasn't entirely sure how to properly integrate it into the rest of the stub generation, so I manually copy-pasted it into the .pyi file. Hopefully this is a good starting point!

One thing to note was the <data> type for StructDef was, in all my testing, inaccessible and so I just assume it's private (even though it's listed as public). All <systemGlobal> types were accessible, so I assume they're public.