--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_workspace/src/settings.rs

@@ -1,6 +1,7 @@
 use path_absolutize::path_dedot;
 use ruff_cache::cache_dir;
 use ruff_formatter::{FormatOptions, IndentStyle, IndentWidth, LineWidth};
+use ruff_linter::display_settings;
 use ruff_linter::settings::types::{
     ExtensionMapping, FilePattern, FilePatternSet, SerializationFormat, UnsafeFixes,
 };
@@ -12,6 +13,7 @@ use ruff_python_formatter::{
     QuoteStyle,
 };
 use ruff_source_file::find_newline;
+use std::fmt;
 use std::path::{Path, PathBuf};
 
 #[derive(Debug, CacheKey)]
@@ -55,6 +57,30 @@ impl Default for Settings {
     }
 }
 
+impl fmt::Display for Settings {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        writeln!(f, "\n# General Settings")?;
+        display_settings! {
+            formatter = f,
+            fields = [
+                // We want the quotes and lossy UTF8 conversion for this path, so
+                // using PathBuf's `Debug` formatter suffices.
+                self.cache_dir     | debug,
+                self.fix,
+                self.fix_only,
+                self.output_format,
+                self.show_fixes,
+                self.show_source,
+                self.unsafe_fixes,
+                self.file_resolver | nested,
+                self.linter        | nested,
+                self.formatter     | nested
+            ]
+        }
+        Ok(())
+    }
+}
+
 #[derive(Debug, CacheKey)]
 pub struct FileResolverSettings {
     pub exclude: FilePatternSet,
@@ -66,6 +92,26 @@ pub struct FileResolverSettings {
     pub project_root: PathBuf,
 }
 
+impl fmt::Display for FileResolverSettings {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        writeln!(f, "\n# File Resolver Settings")?;
+        display_settings! {
+            formatter = f,
+            namespace = "file_resolver",
+            fields = [
+                self.exclude,
+                self.extend_exclude,
+                self.force_exclude,
+                self.include,
+                self.extend_include,
+                self.respect_gitignore,
+                self.project_root | debug,
+            ]
+        }
+        Ok(())
+    }
+}
+
 pub(crate) static EXCLUDE: &[FilePattern] = &[
     FilePattern::Builtin(".bzr"),
     FilePattern::Builtin(".direnv"),
@@ -195,6 +241,30 @@ impl Default for FormatterSettings {
     }
 }
 
+impl fmt::Display for FormatterSettings {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        writeln!(f, "\n# Formatter Settings")?;
+        display_settings! {
+            formatter = f,
+            namespace = "formatter",
+            fields = [
+                self.exclude,
+                self.target_version | debug,
+                self.preview,
+                self.line_width,
+                self.line_ending,
+                self.indent_style,
+                self.indent_width,
+                self.quote_style,
+                self.magic_trailing_comma,
+                self.docstring_code_format,
+                self.docstring_code_line_width,
+            ]
+        }
+        Ok(())
+    }
+}
+
 #[derive(
     Copy, Clone, Debug, Eq, PartialEq, Default, CacheKey, serde::Serialize, serde::Deserialize,
 )]
@@ -216,3 +286,14 @@ pub enum LineEnding {
     /// Line endings will be converted to `\n` on Unix and `\r\n` on Windows.
     Native,
 }
+
+impl fmt::Display for LineEnding {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Auto => write!(f, "auto"),
+            Self::Lf => write!(f, "lf"),
+            Self::CrLf => write!(f, "crlf"),
+            Self::Native => write!(f, "native"),
+        }
+    }
+}