Make git panel entries clickable (#22329)

Makes a first pass over git panel UI, making it more interactive.


![image](https://github.com/user-attachments/assets/4d43b086-4ef2-4913-9783-2b9467d99c9a)


* every item can be selected, the selection is shown in the panel
* every item can be clicked, which changes the selection and
creates/focuses the editor with a project changes multi buffer
* the editor is scrolled so that the clicked item is in the center
* it's possible to nagivate up and down the panel, selecting
next/previous items in it, triggering the editor scroll

Known issues:

* entries are updated oddly sometimes (should become better after
DiffMap improvements land?)
* only unstaged diffs are shown currently (entry status storage should
help with this)
* no deleted files are displayed (the underlying work is done by others
now)
* added files have no diff hunks shown (DiffMap will have it?)
* performance story has not improved (again, DiffMap and status storage
should help with this)

Release Notes:

- N/A

crates/editor/src/editor.rs

@@ -128,6 +128,7 @@ use multi_buffer::{
     ExpandExcerptDirection, MultiBufferDiffHunk, MultiBufferPoint, MultiBufferRow, ToOffsetUtf16,
 };
 use project::{
+    buffer_store::BufferChangeSet,
     lsp_store::{FormatTarget, FormatTrigger, OpenLspBufferHandle},
     project_settings::{GitGutterSetting, ProjectSettings},
     CodeAction, Completion, CompletionIntent, DocumentHighlight, InlayHint, Location, LocationLink,
@@ -12950,6 +12951,14 @@ impl Editor {
             .and_then(|item| item.to_any().downcast_ref::<T>())
     }
 
+    pub fn add_change_set(
+        &mut self,
+        change_set: Model<BufferChangeSet>,
+        cx: &mut ViewContext<Self>,
+    ) {
+        self.diff_map.add_change_set(change_set, cx);
+    }
+
     fn character_size(&self, cx: &mut ViewContext<Self>) -> gpui::Point<Pixels> {
         let text_layout_details = self.text_layout_details(cx);
         let style = &text_layout_details.editor_style;