Add other godot auto-generated files to gitignore.

[Ivorforce]

Referring to how godot-cpp does it: https://github.com/godotengine/godot-cpp/blob/d47758910428242169ebe59329b449edf16036e0/.gitignore

[dsnopek]

Er, hang on, I didn't notice this was multiple commits. This'll need to be squashed to a single commit before it can be merged.

See https://docs.godotengine.org/en/latest/contributing/workflow/pr_workflow.html#the-interactive-rebase

[Ivorforce]

@paddy-exe done

[paddy-exe]

Thanks!