ruff_python_formatter: add docstring-code-line-width internal setting (#9055)

## Summary

This does the light plumbing necessary to add a new internal option that
permits setting the line width of code examples in docstrings. The plan
is to add the corresponding user facing knob in #8854.

Note that this effectively removes the `same-as-global` configuration
style discussed [in this
comment](https://github.com/astral-sh/ruff/issues/8855#issuecomment-1847230440).
It replaces it with the `{integer}` configuration style only.

There are a lot of commits here, but they are each tiny to make review
easier because of the changes to snapshots.

## Test Plan

I added a new docstring test configuration that sets
`docstring-code-line-width = 60` and examined the differences.

crates/ruff_python_formatter/src/expression/string/docstring.rs

@@ -464,6 +464,7 @@ impl<'ast, 'buf, 'fmt, 'src> DocstringLinePrinter<'ast, 'buf, 'fmt, 'src> {
             .f
             .options()
             .clone()
+            .with_line_width(self.f.options().docstring_code_line_width())
             // It's perhaps a little odd to be hard-coding the indent
             // style here, but I believe it is necessary as a result
             // of the whitespace normalization otherwise done in