C#: Use HashCode.Combine() for basic composite types instead of xor

[jaros3]

Vector2I.GetHashCode() creates hash conflicts if X and Y concide:
(0, 0) => 0.GetHashCode() ^ 0.GetHashCode() == 0
(1, 1) => 1.GetHashCode() ^ 1.GetHashCode() == 0
(2, 2) => 2.GetHashCode() ^ 2.GetHashCode() == 0

Let's use HashCode.Combine(X, Y) instead. It will combine hash codes properly and minimize conflicts.

[AThousandShips]

This differs from all the other vectors, and all other types in fact

If this is to be done it needs to be done completely

[AThousandShips]

This is not all cases either, you're missing AABB, Basis, Rect2(I), Transform2/3D, Quaternion, Plane, Projection

[RedworkDE]

LGTM

[akien-mga]

For the record, your commit seems not to be linked to your GitHub account. See: Why are my commits linked to the wrong user? for more info.

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉

Remember to add the email used for this commit as secondary email in your GitHub profile, if you want to claim this commit as authored by your GitHub account. Otherwise your next PR will still show as "First-time contributor".