Add line ending selector (#35392)

Partially addresses this issue #5294

Adds a selector between `LF` and `CRLF` for the buffer's line endings,
the checkmark denotes the currently selected line ending.

Selector
<img width="487" height="66" alt="image"
src="https://github.com/user-attachments/assets/13f2480f-4d2d-4afe-adf5-385aeb421393"
/>

Release Notes:

- Added line ending selector.

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/language/src/buffer_tests.rs

@@ -67,6 +67,78 @@ fn test_line_endings(cx: &mut gpui::App) {
     });
 }
 
+#[gpui::test]
+fn test_set_line_ending(cx: &mut TestAppContext) {
+    let base = cx.new(|cx| Buffer::local("one\ntwo\nthree\n", cx));
+    let base_replica = cx.new(|cx| {
+        Buffer::from_proto(1, Capability::ReadWrite, base.read(cx).to_proto(cx), None).unwrap()
+    });
+    base.update(cx, |_buffer, cx| {
+        cx.subscribe(&base_replica, |this, _, event, cx| {
+            if let BufferEvent::Operation {
+                operation,
+                is_local: true,
+            } = event
+            {
+                this.apply_ops([operation.clone()], cx);
+            }
+        })
+        .detach();
+    });
+    base_replica.update(cx, |_buffer, cx| {
+        cx.subscribe(&base, |this, _, event, cx| {
+            if let BufferEvent::Operation {
+                operation,
+                is_local: true,
+            } = event
+            {
+                this.apply_ops([operation.clone()], cx);
+            }
+        })
+        .detach();
+    });
+
+    // Base
+    base_replica.read_with(cx, |buffer, _| {
+        assert_eq!(buffer.line_ending(), LineEnding::Unix);
+    });
+    base.update(cx, |buffer, cx| {
+        assert_eq!(buffer.line_ending(), LineEnding::Unix);
+        buffer.set_line_ending(LineEnding::Windows, cx);
+        assert_eq!(buffer.line_ending(), LineEnding::Windows);
+    });
+    base_replica.read_with(cx, |buffer, _| {
+        assert_eq!(buffer.line_ending(), LineEnding::Windows);
+    });
+    base.update(cx, |buffer, cx| {
+        buffer.set_line_ending(LineEnding::Unix, cx);
+        assert_eq!(buffer.line_ending(), LineEnding::Unix);
+    });
+    base_replica.read_with(cx, |buffer, _| {
+        assert_eq!(buffer.line_ending(), LineEnding::Unix);
+    });
+
+    // Replica
+    base.read_with(cx, |buffer, _| {
+        assert_eq!(buffer.line_ending(), LineEnding::Unix);
+    });
+    base_replica.update(cx, |buffer, cx| {
+        assert_eq!(buffer.line_ending(), LineEnding::Unix);
+        buffer.set_line_ending(LineEnding::Windows, cx);
+        assert_eq!(buffer.line_ending(), LineEnding::Windows);
+    });
+    base.read_with(cx, |buffer, _| {
+        assert_eq!(buffer.line_ending(), LineEnding::Windows);
+    });
+    base_replica.update(cx, |buffer, cx| {
+        buffer.set_line_ending(LineEnding::Unix, cx);
+        assert_eq!(buffer.line_ending(), LineEnding::Unix);
+    });
+    base.read_with(cx, |buffer, _| {
+        assert_eq!(buffer.line_ending(), LineEnding::Unix);
+    });
+}
+
 #[gpui::test]
 fn test_select_language(cx: &mut App) {
     init_settings(cx, |_| {});