--show-settings displays active settings in a far more readable format (#9464)

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## Summary

Fixes #8334.

`Display` has been implemented for `ruff_workspace::Settings`, which
gives a much nicer and more readable output to `--show-settings`.

Internally, a `display_settings` utility macro has been implemented to
reduce the boilerplate of the display code.

### Work to be done

- [x] A lot of formatting for `Vec<_>` and `HashSet<_>` types have been
stubbed out, using `Debug` as a fallback. There should be a way to add
generic formatting support for these types as a modifier in
`display_settings`.
- [x] Several complex types were also stubbed out and need proper
`Display` implementations rather than falling back on `Debug`.
- [x] An open question needs to be answered: how important is it that
the output be valid TOML? Some types in settings, such as a hash-map
from a glob pattern to a multi-variant enum, will be hard to rework into
valid _and_ readable TOML.
- [x] Tests need to be implemented.

## Test Plan

Tests consist of a snapshot test for the default `--show-settings`
output and a doctest for `display_settings!`.

crates/ruff_formatter/src/lib.rs

@@ -35,6 +35,7 @@ mod source_code;
 use crate::formatter::Formatter;
 use crate::group_id::UniqueGroupIdBuilder;
 use crate::prelude::TagKind;
+use std::fmt;
 use std::fmt::{Debug, Display};
 use std::marker::PhantomData;
 use std::num::{NonZeroU16, NonZeroU8, TryFromIntError};
@@ -113,6 +114,12 @@ impl Default for IndentWidth {
     }
 }
 
+impl Display for IndentWidth {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        Display::fmt(&self.0, f)
+    }
+}
+
 impl TryFrom<u8> for IndentWidth {
     type Error = TryFromIntError;
 
@@ -146,6 +153,12 @@ impl Default for LineWidth {
     }
 }
 
+impl Display for LineWidth {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        Display::fmt(&self.0, f)
+    }
+}
+
 impl TryFrom<u16> for LineWidth {
     type Error = TryFromIntError;