Merge MutableAppContext into AppContext

There may have been a good reason for the difference at some point, or I was
still learning Rust. But now it's just &mut AppContext vs &AppContext.

crates/terminal_view/src/terminal_button.rs

@@ -1,7 +1,7 @@
 use context_menu::{ContextMenu, ContextMenuItem};
 use gpui::{
     elements::*, impl_internal_actions, CursorStyle, Element, ElementBox, Entity, MouseButton,
-    MutableAppContext, RenderContext, View, ViewContext, ViewHandle, WeakModelHandle,
+    AppContext, RenderContext, View, ViewContext, ViewHandle, WeakModelHandle,
     WeakViewHandle,
 };
 use settings::Settings;
@@ -21,7 +21,7 @@ pub struct FocusTerminal {
 
 impl_internal_actions!(terminal, [FocusTerminal, DeployTerminalMenu]);
 
-pub fn init(cx: &mut MutableAppContext) {
+pub fn init(cx: &mut AppContext) {
     cx.add_action(TerminalButton::deploy_terminal_menu);
     cx.add_action(TerminalButton::focus_terminal);
 }

crates/terminal_view/src/terminal_view.rs

@@ -16,8 +16,8 @@ use gpui::{
     geometry::vector::Vector2F,
     impl_actions, impl_internal_actions,
     keymap_matcher::{KeymapContext, Keystroke},
-    AnyViewHandle, AppContext, Element, ElementBox, Entity, ModelHandle, MutableAppContext, Task,
-    View, ViewContext, ViewHandle, WeakViewHandle,
+    AnyViewHandle, AppContext, Element, ElementBox, Entity, ModelHandle, Task, View, ViewContext,
+    ViewHandle, WeakViewHandle,
 };
 use project::{LocalWorktree, Project};
 use serde::Deserialize;
@@ -68,7 +68,7 @@ impl_actions!(terminal, [SendText, SendKeystroke]);
 
 impl_internal_actions!(project_panel, [DeployContextMenu]);
 
-pub fn init(cx: &mut MutableAppContext) {
+pub fn init(cx: &mut AppContext) {
     cx.add_action(TerminalView::deploy);
 
     register_deserializable_item::<TerminalView>(cx);