gpui: Improve Anchored to support center position (#47154)

Release Notes:

- N/A

Ref https://github.com/longbridge/gpui-component/pull/1956 extract my
fork version of `anchored.rs` to let GPUI to support position Anchored
at center.


https://github.com/user-attachments/assets/8d0230ed-4b75-440b-b8c3-9bde3decd141

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/git_graph/src/git_graph.rs

@@ -11,7 +11,7 @@ use git::{
 };
 use git_ui::{commit_tooltip::CommitAvatar, commit_view::CommitView, git_status_icon};
 use gpui::{
-    AnyElement, App, Bounds, ClickEvent, ClipboardItem, Corner, DefiniteLength, DragMoveEvent,
+    Anchor, AnyElement, App, Bounds, ClickEvent, ClipboardItem, DefiniteLength, DragMoveEvent,
     ElementId, Empty, Entity, EventEmitter, FocusHandle, Focusable, Hsla, PathBuilder, Pixels,
     Point, ScrollStrategy, ScrollWheelEvent, SharedString, Subscription, Task, TextStyleRefinement,
     UniformListScrollHandle, WeakEntity, Window, actions, anchored, deferred, point, prelude::*,
@@ -2863,7 +2863,7 @@ impl Render for GitGraph {
                 deferred(
                     anchored()
                         .position(*position)
-                        .anchor(Corner::TopLeft)
+                        .anchor(Anchor::TopLeft)
                         .child(menu.clone()),
                 )
                 .with_priority(1)