Pass a MutableAppContext to Element::layout and ::dispatch_event

We need to mutate the app in these cases to relay layout state, so this just makes things easier. We won't be able to perform layout in parallel but it's questionable whether we'll ever actually do that. If we do, we can revisit.

Co-Authored-By: Antonio Scandurra <me@as-cii.com>
Co-Authored-By: Max Brunsfeld <maxbrunsfeld@gmail.com>

gpui/src/elements/mouse_event_handler.rs

@@ -24,7 +24,7 @@ impl MouseEventHandler {
         F: FnOnce(MouseState) -> ElementBox,
     {
         let state_handle = cx.value::<Tag, _>(id);
-        let state = state_handle.read(cx, |state| *state);
+        let state = state_handle.read(cx.as_ref(), |state| *state);
         let child = render_child(state);
         Self {
             state: state_handle,
@@ -81,7 +81,7 @@ impl Element for MouseEventHandler {
 
         let handled_in_child = self.child.dispatch_event(event, cx);
 
-        self.state.update(cx.app, |state| match event {
+        self.state.update(cx, |state, cx| match event {
             Event::MouseMoved { position } => {
                 let mouse_in = bounds.contains_point(*position);
                 if state.hovered != mouse_in {

gpui/src/elements/uniform_list.rs

@@ -1,6 +1,5 @@
 use super::{
-    AfterLayoutContext, AppContext, Element, Event, EventContext, LayoutContext, PaintContext,
-    SizeConstraint,
+    AfterLayoutContext, Element, Event, EventContext, LayoutContext, PaintContext, SizeConstraint,
 };
 use crate::{
     geometry::{
@@ -8,7 +7,7 @@ use crate::{
         vector::{vec2f, Vector2F},
     },
     json::{self, json},
-    ElementBox,
+    AppContext, ElementBox,
 };
 use json::ToJson;
 use parking_lot::Mutex;