Highlight merge conflicts and provide for resolving them (#28065)

TODO:

- [x] Make it work in the project diff:
  - [x] Support non-singleton buffers
  - [x] Adjust excerpt boundaries to show full conflicts
- [x] Write tests for conflict-related events and state management
- [x] Prevent hunk buttons from appearing inside conflicts
- [x] Make sure it works over SSH, collab
- [x] Allow separate theming of markers

Bonus:

- [ ] Count of conflicts in toolbar
- [ ] Keyboard-driven navigation and resolution
- [ ] ~~Inlay hints to contextualize "ours"/"theirs"~~

Release Notes:

- Implemented initial support for resolving merge conflicts.

---------

Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/go_to_line/src/go_to_line.rs

@@ -2,7 +2,8 @@ pub mod cursor_position;
 
 use cursor_position::{LineIndicatorFormat, UserCaretPosition};
 use editor::{
-    Anchor, Editor, MultiBufferSnapshot, ToOffset, ToPoint, actions::Tab, scroll::Autoscroll,
+    Anchor, Editor, MultiBufferSnapshot, RowHighlightOptions, ToOffset, ToPoint, actions::Tab,
+    scroll::Autoscroll,
 };
 use gpui::{
     App, DismissEvent, Entity, EventEmitter, FocusHandle, Focusable, Render, SharedString, Styled,
@@ -180,7 +181,10 @@ impl GoToLine {
             editor.highlight_rows::<GoToLineRowHighlights>(
                 start..end,
                 cx.theme().colors().editor_highlighted_line_background,
-                true,
+                RowHighlightOptions {
+                    autoscroll: true,
+                    ..Default::default()
+                },
                 cx,
             );
             editor.request_autoscroll(Autoscroll::center(), cx);