### What does this PR do?
Fixes#23489
The YAML parser was incorrectly treating `...` inside double-quoted
strings as document end markers, causing parse errors for strings
containing ellipsis, particularly affecting internationalized text.
### Example of the bug:
```yaml
balance: "👛 لا تمتلك محفظة... !"
```
This would fail with: `error: Unexpected document end`
### Root cause:
The bug was introduced in commit fcbd57ac48 which attempted to optimize
document marker detection by using `self.line_indent == .none` instead
of tracking newlines with a local flag. However, this check was
incomplete - it didn't track whether we had just processed a newline
character.
### The fix:
Restored the `nl` (newline) flag pattern from the single-quoted scanner
and combined it with the `line_indent` check. Document markers `...` and
`---` are now only recognized when **all** of these conditions are met:
1. We're after a newline (`nl == true`)
2. We're at column 0 (`self.line_indent == .none`)
3. Followed by whitespace or EOF
This allows `...` to appear freely in double-quoted strings while still
correctly recognizing actual document end markers at the start of lines.
### How did you verify your code works?
1. Reproduced the original issue from #23489
2. Applied the fix and verified all test cases pass:
- Original Arabic text with emoji: `"👛 لا تمتلك محفظة... !"`
- Various `...` positions: start, middle, end
- Both single and double quotes
- Multiline strings with indented `...` (issue #22392)
3. Created regression test in `test/regression/issue/23489.test.ts`
4. Verified existing YAML tests still pass (514 pass, up from 513)
cc @dylan-conway for review
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
