Fixes file path errors, Vulkan related material updates, and other errors

[addmix]

Still non-functional, currently CTDT with no error whenever the plugin in enabled.

[HungryProton]

Hi, thanks for the PR!

Yes, the plugin doesn't work even with the GDScript updates, looks like I forgot to push the v4 branch in a while. I'm rewriting the core part of the plugin to fix the bad decisions I made with the Godot 3 version and upgrading the UX a bit. The modifier scripts probably won't change much, but everything else will, including the inspector plugins.

No ETA yet.

[addmix]

Can you push what you have so far?

[HungryProton]

Still need a lot of cleaning, and some features and completely missing for now. I'll post an update once I have a basic version working.