Unify string parameters across all builders

[chitoyuu]

Created during survey of commented code (#377).

As of Rust 1.63.0, the turbofish syntax can now be used along with impl Trait: https://blog.rust-lang.org/2022/08/11/Rust-1.63.0.html#turbofish-for-generics-in-functions-with-impl-trait

As such, we now have more freedom to use types like impl Into<GodotString> or impl Into<Cow<'a, str>> where we need to take string arguments (for names) along with explicit type arguments in builders.

This may still constitute a breaking change, if a technical one.