Rework diff rendering to allow putting the cursor into deleted text, soft-wrapping and scrolling deleted text correctly (#22994)

Closes #12553

* [x] Fix `diff_hunk_before`
* [x] Fix failure to show deleted text when expanding hunk w/ cursor on
second line of the hunk
* [x] Failure to expand diff hunk below the cursor.
* [x] Delete the whole file, and expand the diff. Backspace over the
deleted hunk, panic!
* [x] Go-to-line now counts the diff hunks, but it should not
* [x] backspace at the beginning of a deleted hunk deletes too much text
* [x] Indent guides are rendered incorrectly 
* [ ] Fix randomized multi buffer tests

Maybe:
* [ ] Buffer search should include deleted text (in vim mode it turns
out I use `/x` all the time to jump to the next x I can see).
* [ ] vim: should refuse to switch into insert mode if selection is
fully within a diff.
* [ ] vim `o` command when cursor is on last line of deleted hunk.
* [ ] vim `shift-o` on first line of deleted hunk moves cursor but
doesn't insert line
* [x] `enter` at end of diff hunk inserts a new line but doesn't move
cursor
* [x] (`shift-enter` at start of diff hunk does nothing)
* [ ] Inserting a line just before an expanded hunk collapses it

Release Notes:


- Improved diff rendering, allowing you to navigate with your cursor
inside of deleted text in diff hunks.

---------

Co-authored-by: Conrad <conrad@zed.dev>
Co-authored-by: Cole <cole@zed.dev>
Co-authored-by: Mikayla <mikayla@zed.dev>
Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>
Co-authored-by: Michael <michael@zed.dev>
Co-authored-by: Agus <agus@zed.dev>
Co-authored-by: João <joao@zed.dev>

crates/editor/src/display_map/inlay_map.rs

@@ -1,7 +1,9 @@
 use crate::{HighlightStyles, InlayId};
 use collections::BTreeSet;
 use language::{Chunk, Edit, Point, TextSummary};
-use multi_buffer::{Anchor, MultiBufferRow, MultiBufferRows, MultiBufferSnapshot, ToOffset};
+use multi_buffer::{
+    Anchor, MultiBufferRow, MultiBufferRows, MultiBufferSnapshot, RowInfo, ToOffset,
+};
 use std::{
     cmp,
     ops::{Add, AddAssign, Range, Sub, SubAssign},
@@ -67,11 +69,11 @@ impl Inlay {
 impl sum_tree::Item for Transform {
     type Summary = TransformSummary;
 
-    fn summary(&self, _cx: &()) -> Self::Summary {
+    fn summary(&self, _: &()) -> Self::Summary {
         match self {
             Transform::Isomorphic(summary) => TransformSummary {
-                input: summary.clone(),
-                output: summary.clone(),
+                input: *summary,
+                output: *summary,
             },
             Transform::Inlay(inlay) => TransformSummary {
                 input: TextSummary::default(),
@@ -362,14 +364,14 @@ impl<'a> InlayBufferRows<'a> {
 }
 
 impl<'a> Iterator for InlayBufferRows<'a> {
-    type Item = Option<u32>;
+    type Item = RowInfo;
 
     fn next(&mut self) -> Option<Self::Item> {
         let buffer_row = if self.inlay_row == 0 {
             self.buffer_rows.next().unwrap()
         } else {
             match self.transforms.item()? {
-                Transform::Inlay(_) => None,
+                Transform::Inlay(_) => Default::default(),
                 Transform::Isomorphic(_) => self.buffer_rows.next().unwrap(),
             }
         };
@@ -448,7 +450,7 @@ impl InlayMap {
                 new_transforms.append(cursor.slice(&buffer_edit.old.start, Bias::Left, &()), &());
                 if let Some(Transform::Isomorphic(transform)) = cursor.item() {
                     if cursor.end(&()).0 == buffer_edit.old.start {
-                        push_isomorphic(&mut new_transforms, transform.clone());
+                        push_isomorphic(&mut new_transforms, *transform);
                         cursor.next(&());
                     }
                 }
@@ -892,7 +894,7 @@ impl InlaySnapshot {
     }
 
     pub fn text_summary(&self) -> TextSummary {
-        self.transforms.summary().output.clone()
+        self.transforms.summary().output
     }
 
     pub fn text_summary_for_range(&self, range: Range<InlayOffset>) -> TextSummary {
@@ -945,7 +947,7 @@ impl InlaySnapshot {
         summary
     }
 
-    pub fn buffer_rows(&self, row: u32) -> InlayBufferRows<'_> {
+    pub fn row_infos(&self, row: u32) -> InlayBufferRows<'_> {
         let mut cursor = self.transforms.cursor::<(InlayPoint, Point)>(&());
         let inlay_point = InlayPoint::new(row, 0);
         cursor.seek(&inlay_point, Bias::Left, &());
@@ -967,7 +969,7 @@ impl InlaySnapshot {
         InlayBufferRows {
             transforms: cursor,
             inlay_row: inlay_point.row(),
-            buffer_rows: self.buffer.buffer_rows(buffer_row),
+            buffer_rows: self.buffer.row_infos(buffer_row),
             max_buffer_row,
         }
     }
@@ -1477,7 +1479,10 @@ mod tests {
         );
         assert_eq!(inlay_snapshot.text(), "|123|\nabc\n|456|def\n|567|\n\nghi");
         assert_eq!(
-            inlay_snapshot.buffer_rows(0).collect::<Vec<_>>(),
+            inlay_snapshot
+                .row_infos(0)
+                .map(|info| info.buffer_row)
+                .collect::<Vec<_>>(),
             vec![Some(0), None, Some(1), None, None, Some(2)]
         );
     }
@@ -1548,7 +1553,7 @@ mod tests {
             }
             assert_eq!(inlay_snapshot.text(), expected_text.to_string());
 
-            let expected_buffer_rows = inlay_snapshot.buffer_rows(0).collect::<Vec<_>>();
+            let expected_buffer_rows = inlay_snapshot.row_infos(0).collect::<Vec<_>>();
             assert_eq!(
                 expected_buffer_rows.len() as u32,
                 expected_text.max_point().row + 1
@@ -1556,7 +1561,7 @@ mod tests {
             for row_start in 0..expected_buffer_rows.len() {
                 assert_eq!(
                     inlay_snapshot
-                        .buffer_rows(row_start as u32)
+                        .row_infos(row_start as u32)
                         .collect::<Vec<_>>(),
                     &expected_buffer_rows[row_start..],
                     "incorrect buffer rows starting at {}",