settings: Use a derive macro for refine (#38451)

When we refactored settings to not pass JSON blobs around, we ended up
needing
to write *a lot* of code that just merged things (like json merge used
to do).

Use a derive macro to prevent typos in this logic.

Release Notes:

- N/A

crates/collections/src/collections.rs

@@ -22,6 +22,7 @@ pub type IndexMap<K, V> = indexmap::IndexMap<K, V>;
 #[cfg(not(feature = "test-support"))]
 pub type IndexSet<T> = indexmap::IndexSet<T>;
 
+pub use indexmap::Equivalent;
 pub use rustc_hash::FxHasher;
 pub use rustc_hash::{FxHashMap, FxHashSet};
 pub use std::collections::*;