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.
* Extensions are now scanned and loaded on demand.
* Extensions found are cached into a file that is used to load them (which is also exported).
* Editor will ask to restart when an extension requires core functionality.
* Editor will attempt to load extensions always before importing or loading scenes. This ensures extensions can register the relevant types.
For the time being we don't support writing a description for those, preferring
having all details in the method's description.
Using self-closing tags saves half the lines, and prevents contributors from
thinking that they should write the argument or return documentation there.
* Deprecates GDNative in favor of a simpler, lower level interface.
* New extension system allows registering core engine classes.
* Simple header interface in gdnative_interace.h
