Support relative line number on wrapped lines (rework) (#41805)

## Add relative line numbers on wrapped lines, take 2

This is a rework of https://github.com/zed-industries/zed/pull/39268
that excludes
https://github.com/zed-industries/zed/pull/39268/commits/e7096d27a6463f6eb7c2a821637c5773b2460c10.
This commit introduced some line number rendering issues as described in
https://github.com/zed-industries/zed/issues/41422.

While @ConradIrwin suggested we try to pass in the buffer rows from the
calling method instead of the snapshot, that
appears to have had unintended consequences and I don't think the two
calculations were intended to do the same thing. Hence, this PR has
removed those changes.

This PR also includes the migration fix originally done by @MrSubidubi
in https://github.com/zed-industries/zed/pull/41351.

## Original PR description and release notes.

**Problem:** Current relative line numbering creates a mismatch with
vim-style navigation when soft wrap is enabled. Users must mentally
calculate whether target lines are wrapped segments or logical lines,
making `<n>j/k` navigation unreliable and cognitively demanding.

**How things work today:**
- Real line navigation (`j/k` moves by logical lines): Requires
determining if visible lines are wrapped segments before jumping. Can't
jump to wrapped lines directly.
- Display line navigation (`j/k` moves by display rows): Line numbers
don't correspond to actual row distances for multi-line jumps.

**Proposed solution:** Count and number each display line (including
wrapped segments) for relative numbering. This creates direct
visual-to-navigational correspondence, where the relative number shown
always matches the `<n>j/k` distance needed.

**Benefits:**
- Eliminates mental overhead of distinguishing wrapped vs. logical lines
- Makes relative line numbers consistently actionable regardless of wrap
state
- Preserves intuitive "what you see is what you navigate" principle
- Maintains vim workflow efficiency in narrow window scenarios

Also explained and discussed in
https://github.com/zed-industries/zed/discussions/25733.

Release Notes:

- Added support for counting wrapped lines as relative lines and for
displaying line numbers for wrapped segments. Changes
`relative_line_numbers` from a boolean to an enum: `enabled`,
`disabled`, or `wrapped`.

crates/multi_buffer/src/multi_buffer.rs

@@ -340,6 +340,7 @@ pub struct RowInfo {
     pub multibuffer_row: Option<MultiBufferRow>,
     pub diff_status: Option<buffer_diff::DiffHunkStatus>,
     pub expand_info: Option<ExpandInfo>,
+    pub wrapped_buffer_row: Option<u32>,
 }
 
 /// A slice into a [`Buffer`] that is being edited in a [`MultiBuffer`].
@@ -6650,6 +6651,7 @@ impl Iterator for MultiBufferRows<'_> {
                 multibuffer_row: Some(MultiBufferRow(0)),
                 diff_status: None,
                 expand_info: None,
+                wrapped_buffer_row: None,
             });
         }
 
@@ -6707,6 +6709,7 @@ impl Iterator for MultiBufferRows<'_> {
                     buffer_row: Some(last_row),
                     multibuffer_row: Some(multibuffer_row),
                     diff_status: None,
+                    wrapped_buffer_row: None,
                     expand_info,
                 });
             } else {
@@ -6751,6 +6754,7 @@ impl Iterator for MultiBufferRows<'_> {
                 .diff_hunk_status
                 .filter(|_| self.point < region.range.end),
             expand_info,
+            wrapped_buffer_row: None,
         });
         self.point += Point::new(1, 0);
         result