Settings refactor (#38367)

Co-Authored-By: Ben K <ben@zed.dev>
Co-Authored-By: Anthony <anthony@zed.dev>
Co-Authored-By: Mikayla <mikayla@zed.dev>

Release Notes:

- settings: Major internal changes to settings. The primary user-facing
effect is that some settings which did not make sense in project
settings files are no-longer read from there. (For example the inline
blame settings)

---------

Co-authored-by: Ben Kunkle <ben@zed.dev>
Co-authored-by: Mikayla Maki <mikayla.c.maki@gmail.com>
Co-authored-by: Anthony <anthony@zed.dev>

crates/util/src/util.rs

@@ -1390,3 +1390,21 @@ Line 3"#
         assert_eq!(result[1], (10..15, "world")); // '🦀' is 4 bytes
     }
 }
+
+pub fn refine<T: Clone>(dest: &mut T, src: &Option<T>) {
+    if let Some(src) = src {
+        *dest = src.clone()
+    }
+}
+
+pub trait MergeFrom: Sized + Clone {
+    fn merge_from(&mut self, src: &Option<Self>);
+}
+
+impl<T: Clone> MergeFrom for T {
+    fn merge_from(&mut self, src: &Option<Self>) {
+        if let Some(src) = src {
+            *self = src.clone();
+        }
+    }
+}