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/settings/src/settings.rs

@@ -1,6 +1,7 @@
 mod base_keymap_setting;
 mod editable_setting_control;
 mod keymap_file;
+pub mod merge_from;
 mod settings_content;
 mod settings_file;
 mod settings_json;
@@ -27,8 +28,7 @@ pub use settings_store::{
     InvalidSettingsError, LocalSettingsKind, Settings, SettingsKey, SettingsLocation, SettingsStore,
 };
 pub use settings_ui_core::*;
-// Re-export the derive macro
-pub use settings_ui_macros::{SettingsKey, SettingsUi};
+
 pub use vscode_import::{VsCodeSettings, VsCodeSettingsSource};
 
 #[derive(Clone, Debug, PartialEq)]