GDExtension: Mark virtual function as is_required in extension_api.json

[dsnopek]

This is a draft exploring how to implement godotengine/godot-proposals#9982

TODO to finish:

• Find all the required virtual methods and swap in the GDVIRTUAL*_REQUIRED() macro
• Replace all GDVIRTUAL_REQUIRED_CALL() with GDVIRTUAL_CALL()

[TitanNano]

@dsnopek I migrated all the remaining instances of GDVIRTUAL_REQUIRED_CALL in e07dbec and removed the macro in 0590f31. You are welcome to add these commits to your PR.

EDIT: they are on this branch: https://github.com/TitanNano/godot/commits/gdextension-required-virtuals/

[dsnopek]

@TitanNano Thanks! I added your changes.

After I've gone through and double-checked all the changes I'll take this out of draft.

[TitanNano]

@dsnopek do you think this can make it into 4.4?

[dsnopek]

This would be great to get into 4.4, especially if we can get PR #86079 too. I'll try to find some time soon to dig back into both PRs.

[dsnopek]

I just rebased, updated for new required virtual methods that have been added, and finally went back through everything and double-checked that everything that should be required is marked as required.

So, I'm taking this one of draft status now!

[Bromeon]

This looks great, thanks so much! I implemented the Rust part and while I haven't had the chance to test individual APIs yet, the is_required field is consistently present for all virtual methods 🙂

Maybe @TitanNano could also have another look?

One question, do you think is_override_required would be clearer than just is_required? Or clear enough from the context?

[akien-mga]

@reduz Can you confirm whether it's fine to add a new method flag?

[akien-mga]

Tried to ask three times but no luck, so let's merge and reduz will tell us if this was incorrect :)

[akien-mga]

Thanks!