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`.

docs/src/vim.md

@@ -606,7 +606,7 @@ Here are a few general Zed settings that can help you fine-tune your Vim experie
 | Property                | Description                                                                                                                                                   | Default Value        |
 | ----------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------- |
 | cursor_blink            | If `true`, the cursor blinks.                                                                                                                                 | `true`               |
-| relative_line_numbers   | If `true`, line numbers in the left gutter are relative to the cursor.                                                                                        | `false`              |
+| relative_line_numbers   | If `"enabled"`, line numbers in the left gutter are relative to the cursor. If `"wrapped"`, they also display for wrapped lines.                              | `"disabled"`         |
 | scrollbar               | Object that controls the scrollbar display. Set to `{ "show": "never" }` to hide the scroll bar.                                                              | `{ "show": "auto" }` |
 | scroll_beyond_last_line | If set to `"one_page"`, allows scrolling up to one page beyond the last line. Set to `"off"` to prevent this behavior.                                        | `"one_page"`         |
 | vertical_scroll_margin  | The number of lines to keep above or below the cursor when scrolling. Set to `0` to allow the cursor to go up to the edges of the screen vertically.          | `3`                  |
@@ -620,7 +620,7 @@ Here's an example of these settings changed:
   // Disable cursor blink
   "cursor_blink": false,
   // Use relative line numbers
-  "relative_line_numbers": true,
+  "relative_line_numbers": "enabled",
   // Hide the scroll bar
   "scrollbar": { "show": "never" },
   // Prevent the buffer from scrolling beyond the last line