Use Rope instead of String for buffer diff base (#11300)

As an attempt to do things better when showing diff hunks, store diff
base as Rope, not String, to have cheaper clones when the diff base text
is reused, e.g. creating another buffer with the diff base text for hunk
diff expanding.

Release Notes:

- N/A

crates/project/src/project.rs

@@ -98,7 +98,7 @@ use std::{
 };
 use task::static_source::{StaticSource, TrackedFile};
 use terminals::Terminals;
-use text::{Anchor, BufferId, LineEnding};
+use text::{Anchor, BufferId, LineEnding, Rope};
 use util::{
     debug_panic, defer,
     http::{HttpClient, Url},
@@ -7586,7 +7586,11 @@ impl Project {
                                     None
                                 } else {
                                     let relative_path = path.strip_prefix(&work_directory).ok()?;
-                                    repo_entry.repo().lock().load_index_text(relative_path)
+                                    repo_entry
+                                        .repo()
+                                        .lock()
+                                        .load_index_text(relative_path)
+                                        .map(Rope::from)
                                 };
                                 Some((buffer, base_text))
                             }
@@ -7614,7 +7618,7 @@ impl Project {
                         .send(proto::UpdateDiffBase {
                             project_id,
                             buffer_id,
-                            diff_base,
+                            diff_base: diff_base.map(|rope| rope.to_string()),
                         })
                         .log_err();
                 }
@@ -8694,7 +8698,7 @@ impl Project {
         this.update(&mut cx, |this, cx| {
             let buffer_id = envelope.payload.buffer_id;
             let buffer_id = BufferId::new(buffer_id)?;
-            let diff_base = envelope.payload.diff_base;
+            let diff_base = envelope.payload.diff_base.map(Rope::from);
             if let Some(buffer) = this
                 .opened_buffers
                 .get_mut(&buffer_id)
@@ -8859,7 +8863,7 @@ impl Project {
                         .send(proto::UpdateDiffBase {
                             project_id,
                             buffer_id: buffer_id.into(),
-                            diff_base: buffer.diff_base().map(Into::into),
+                            diff_base: buffer.diff_base().map(ToString::to_string),
                         })
                         .log_err();