Add Corner to geometry and make names of corner methods consistent (#22119)

Release Notes:

- N/A

crates/editor/src/hunk_diff.rs

@@ -1,8 +1,7 @@
 use collections::{HashMap, HashSet};
 use git::diff::DiffHunkStatus;
 use gpui::{
-    Action, AnchorCorner, AppContext, CursorStyle, Hsla, Model, MouseButton, Subscription, Task,
-    View,
+    Action, AppContext, Corner, CursorStyle, Hsla, Model, MouseButton, Subscription, Task, View,
 };
 use language::{Buffer, BufferId, Point};
 use multi_buffer::{
@@ -743,7 +742,7 @@ impl Editor {
                                                                 },
                                                             ),
                                                         )
-                                                        .anchor(AnchorCorner::TopRight)
+                                                        .anchor(Corner::TopRight)
                                                         .with_handle(hunk_controls_menu_handle)
                                                         .menu(move |cx| {
                                                             let focus = focus.clone();