--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_linter/src/registry/rule_set.rs

@@ -1,6 +1,6 @@
 use crate::registry::Rule;
 use ruff_macros::CacheKey;
-use std::fmt::{Debug, Formatter};
+use std::fmt::{Debug, Display, Formatter};
 use std::iter::FusedIterator;
 
 const RULESET_SIZE: usize = 13;
@@ -269,6 +269,21 @@ impl Debug for RuleSet {
     }
 }
 
+impl Display for RuleSet {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        if self.is_empty() {
+            write!(f, "[]")?;
+        } else {
+            writeln!(f, "[")?;
+            for rule in self {
+                writeln!(f, "\t{rule:?},")?;
+            }
+            write!(f, "]")?;
+        }
+        Ok(())
+    }
+}
+
 impl FromIterator<Rule> for RuleSet {
     fn from_iter<T: IntoIterator<Item = Rule>>(iter: T) -> Self {
         let mut set = RuleSet::empty();