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/configuring-zed.md

@@ -2994,11 +2994,33 @@ List of `string` glob patterns
 
 - Description: Whether to show relative line numbers in the gutter
 - Setting: `relative_line_numbers`
-- Default: `false`
+- Default: `"disabled"`
 
 **Options**
 
-`boolean` values
+1. Show relative line numbers in the gutter whilst counting wrapped lines as one line:
+
+```json [settings]
+{
+  "relative_line_numbers": "enabled"
+}
+```
+
+2. Show relative line numbers in the gutter, including wrapped lines in the counting:
+
+```json [settings]
+{
+  "relative_line_numbers": "wrapped"
+}
+```
+
+2. Do not use relative line numbers:
+
+```json [settings]
+{
+  "relative_line_numbers": "disabled"
+}
+```
 
 ## Remove Trailing Whitespace On Save