Low-hanging consistency fruits

[Bromeon]

This is a very cosmetic issue, and not urgent at all 🙂

The engine often uses different representations for the same thing. In some cases that's OK or would be hard to change, but in others it's a special case in codegen that may be simple to add. Just to brainstorm, doesn't mean we change all those:

Instance IDs

We have InstanceId, ObjectID (native structs, wraps u64), raw u64, raw i64, EncodedObjectAsID...

• Occurrences of instance_id
• Ideally we can replace everything with InstanceId
• Heuristic: methods ending in _instance_id that return u64 or have an id: u64 parameter.

Intly typed enums

• Object::connect_ex() takes u32, despite ConnectFlags existing.
• Signal::connect() takes i64.
• SceneTree::call_group_flags expects i64 as flag, not GroupCallFlags #185

Duplicated types in manual and generated code

We already handled some (Side, Corner, Vector2Axis, Vector3Axis), there are a few remaining:

• GDExtension.InitializationLevel vs. InitLevel
• ObjectId vs InstanceId

They don't necessarily need to be de-duplicated, but we could at least provide conversions.

Misc

• _count methods (get/set) mostly use i32
  • unclear if usize is an option, although it's currently unsupported. Might be better to stick to i32, as it's not really inconsistent, just a bit harder to integrate with Rust.