Page dedicated to borrowing, re-entrancy and common patterns

[Bromeon]

Users are repeatedly confused about bind/bind_mut, base/base_mut, how to make Rust -> Godot -> Rust calls work, etc. While we do have existing docs about binding and reborrowing, they could be more detailed, motivated by real-world examples.

For inspiration, see:

• DisplayServer singleton error (windows) gdext#1157 (comment)