Preserve cursor position when resetting excerpts (#27850)

Release Notes:

- N/A

---------

Co-authored-by: Nathan Sobo <nathan@zed.dev>
Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/editor/src/test/editor_test_context.rs

@@ -120,10 +120,9 @@ impl EditorTestContext {
                 let buffer = cx.new(|cx| Buffer::local(text, cx));
                 multibuffer.push_excerpts(
                     buffer,
-                    ranges.into_iter().map(|range| ExcerptRange {
-                        context: range,
-                        primary: None,
-                    }),
+                    ranges
+                        .into_iter()
+                        .map(|range| ExcerptRange::new(range.clone())),
                     cx,
                 );
             }