## 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.
4b0fa5f270