Introduce AST nodes for PatternMatchClass arguments (#6881)

## Summary

This PR introduces two new AST nodes to improve the representation of
`PatternMatchClass`. As a reminder, `PatternMatchClass` looks like this:

```python
case Point2D(0, 0, x=1, y=2):
  ...
```

Historically, this was represented as a vector of patterns (for the `0,
0` portion) and parallel vectors of keyword names (for `x` and `y`) and
values (for `1` and `2`). This introduces a bunch of challenges for the
formatter, but importantly, it's also really different from how we
represent similar nodes, like arguments (`func(0, 0, x=1, y=2)`) or
parameters (`def func(x, y)`).

So, firstly, we now use a single node (`PatternArguments`) for the
entire parenthesized region, making it much more consistent with our
other nodes. So, above, `PatternArguments` would be `(0, 0, x=1, y=2)`.

Secondly, we now have a `PatternKeyword` node for `x=1` and `y=2`. This
is much more similar to the how `Keyword` is represented within
`Arguments` for call expressions.

Closes https://github.com/astral-sh/ruff/issues/6866.

Closes https://github.com/astral-sh/ruff/issues/6880.

crates/ruff_python_ast/src/comparable.rs

@@ -153,6 +153,36 @@ impl<'a> From<&'a ast::WithItem> for ComparableWithItem<'a> {
     }
 }
 
+#[derive(Debug, PartialEq, Eq, Hash)]
+pub struct ComparablePatternArguments<'a> {
+    patterns: Vec<ComparablePattern<'a>>,
+    keywords: Vec<ComparablePatternKeyword<'a>>,
+}
+
+impl<'a> From<&'a ast::PatternArguments> for ComparablePatternArguments<'a> {
+    fn from(parameters: &'a ast::PatternArguments) -> Self {
+        Self {
+            patterns: parameters.patterns.iter().map(Into::into).collect(),
+            keywords: parameters.keywords.iter().map(Into::into).collect(),
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Hash)]
+pub struct ComparablePatternKeyword<'a> {
+    attr: &'a str,
+    pattern: ComparablePattern<'a>,
+}
+
+impl<'a> From<&'a ast::PatternKeyword> for ComparablePatternKeyword<'a> {
+    fn from(keyword: &'a ast::PatternKeyword) -> Self {
+        Self {
+            attr: keyword.attr.as_str(),
+            pattern: (&keyword.pattern).into(),
+        }
+    }
+}
+
 #[derive(Debug, PartialEq, Eq, Hash)]
 pub struct PatternMatchValue<'a> {
     value: ComparableExpr<'a>,
@@ -178,9 +208,7 @@ pub struct PatternMatchMapping<'a> {
 #[derive(Debug, PartialEq, Eq, Hash)]
 pub struct PatternMatchClass<'a> {
     cls: ComparableExpr<'a>,
-    patterns: Vec<ComparablePattern<'a>>,
-    kwd_attrs: Vec<&'a str>,
-    kwd_patterns: Vec<ComparablePattern<'a>>,
+    arguments: ComparablePatternArguments<'a>,
 }
 
 #[derive(Debug, PartialEq, Eq, Hash)]
@@ -240,18 +268,12 @@ impl<'a> From<&'a ast::Pattern> for ComparablePattern<'a> {
                 patterns: patterns.iter().map(Into::into).collect(),
                 rest: rest.as_deref(),
             }),
-            ast::Pattern::MatchClass(ast::PatternMatchClass {
-                cls,
-                patterns,
-                kwd_attrs,
-                kwd_patterns,
-                ..
-            }) => Self::MatchClass(PatternMatchClass {
-                cls: cls.into(),
-                patterns: patterns.iter().map(Into::into).collect(),
-                kwd_attrs: kwd_attrs.iter().map(ast::Identifier::as_str).collect(),
-                kwd_patterns: kwd_patterns.iter().map(Into::into).collect(),
-            }),
+            ast::Pattern::MatchClass(ast::PatternMatchClass { cls, arguments, .. }) => {
+                Self::MatchClass(PatternMatchClass {
+                    cls: cls.into(),
+                    arguments: arguments.into(),
+                })
+            }
             ast::Pattern::MatchStar(ast::PatternMatchStar { name, .. }) => {
                 Self::MatchStar(PatternMatchStar {
                     name: name.as_deref(),