Render a diagnostic for syntax errors introduced in formatter tests

[ntBre]

Summary

I spun this out from #21005 because I thought it might be helpful separately. It just renders a nice Diagnostic for syntax errors pointing to the source of the error. This seemed a bit more helpful to me than just the byte offset when working on #21005, and we had most of the code around after #20443 anyway.

Test Plan

This doesn't actually affect any passing tests, but here's an example of the additional output I got when I broke the spacing after the in token:

    error[internal-error]: Expected 'in', found name
      --> /home/brent/astral/ruff/crates/ruff_python_formatter/resources/test/fixtures/black/cases/cantfit.py:50:79
       |
    48 |     need_more_to_make_the_line_long_enough,
    49 | )
    50 | del ([], name_1, name_2), [(), [], name_4, name_3], name_1[[name_2 for name_1 inname_0]]
       |                                                                               ^^^^^^^^
    51 | del ()
       |

I just appended this to the other existing output for now.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

Formatter (stable)

✅ ecosystem check detected no format changes.

Formatter (preview)

✅ ecosystem check detected no format changes.

[MichaReiser]

just the byte offset when working on #21005, and we had most of the code around after #20443 anyway.

Nice! Haha, I installed a hex viewer just for formatter errors