godotengine
C#: Enable nullable environment for `GodotTools`
Enables nullability in majority of GodotTools projects. At first I didn't think this would be possible without GodotSharp getting nullable first (see #83117), but it turns out there was quite a lot that could be setup as-is! The only real area that didn't get expanded upon were certain GodotObject fields (mirroring the selectively disabled nullability seen on a handful of files beforehand), which is likely to be more feasible when GodotSharp gets full-project nullability.
Updated to include GodotTools.IdeMessaging as well; while it's still a touchy file, I realized that it was perfectly safe to upgrade to C# 9 without issue, which does include nullability!
Could you please rebase on the current master? We had an issue with macOS builds which failed your CI.
