Remove initialize from the Element trait (#3338)

Initially, we imagined registering keyboard handlers in the initialize
phase so we would understand the relationships between focus handles
during the layout pass, which would allow us to assign assign `focus_in`
styles that impact layout.

However, we soon realized that many elements aren't created until paint
time anyway, such as within the uniform list. Since it's impossible to
know prior to paint whether an element contains the focused element, it
makes more sense to eliminate the `focus_in` styling helper.

Release Notes:

- N/A

crates/editor2/src/element.rs

@@ -2398,21 +2398,14 @@ impl Element<Editor> for EditorElement {
         Some(self.editor_id.into())
     }
 
-    fn initialize(
+    fn layout(
         &mut self,
         editor: &mut Editor,
         element_state: Option<Self::ElementState>,
         cx: &mut gpui::ViewContext<Editor>,
-    ) -> Self::ElementState {
+    ) -> (gpui::LayoutId, Self::ElementState) {
         editor.style = Some(self.style.clone()); // Long-term, we'd like to eliminate this.
-    }
 
-    fn layout(
-        &mut self,
-        editor: &mut Editor,
-        element_state: &mut Self::ElementState,
-        cx: &mut gpui::ViewContext<Editor>,
-    ) -> gpui::LayoutId {
         let rem_size = cx.rem_size();
         let mut style = Style::default();
         style.size.width = relative(1.).into();
@@ -2421,7 +2414,8 @@ impl Element<Editor> for EditorElement {
             EditorMode::AutoHeight { .. } => todo!(),
             EditorMode::Full => relative(1.).into(),
         };
-        cx.request_layout(&style, None)
+        let layout_id = cx.request_layout(&style, None);
+        (layout_id, ())
     }
 
     fn paint(