Adds VideoStream and relevant resource loaders to migrate
external GDNative plugins to GDExtension.
Adds a VideoStreamLoader as a specialization of ResourceFormatLoader
as ClassDB::is_parent_class is inaccessible from GDExtension currently.
Using Object* instead of Ref<T> in order to avoid the refcount bug
(godotengine/godot-cpp#652)
Also another bug is in ResourceLoader in use on the extension side that
requires fixing.
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.
We already removed it from the online docs with #35132.
Currently it can only be "Built-In Types" (Variant types) or "Core"
(everything else), which is of limited use.
We might also want to consider dropping it from `ClassDB` altogether
in Godot 4.0.
