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_formatter/tests/snapshots/black_compatibility@py_310__pattern_matching_style.py.snap

@@ -65,15 +65,7 @@ match match(
 ```diff
 --- Black
 +++ Ruff
-@@ -6,30 +6,35 @@
-     ):
-         print(1)
-     case c(
--        very_complex=True,
--        perhaps_even_loooooooooooooooooooooooooooooooooooooong=-1,
-+        very_complex=True, perhaps_even_loooooooooooooooooooooooooooooooooooooong=-1
-     ):
-         print(2)
+@@ -13,20 +13,26 @@
      case a:
          pass
  
@@ -103,10 +95,6 @@ match match(
  re.match()
  match match():
      case case(
--        arg,  # comment
-+        arg  # comment
-     ):
-         pass
 ```
 
 ## Ruff Output
@@ -120,7 +108,8 @@ match something:
     ):
         print(1)
     case c(
-        very_complex=True, perhaps_even_loooooooooooooooooooooooooooooooooooooong=-1
+        very_complex=True,
+        perhaps_even_loooooooooooooooooooooooooooooooooooooong=-1,
     ):
         print(2)
     case a:
@@ -149,7 +138,7 @@ re.match(
 re.match()
 match match():
     case case(
-        arg  # comment
+        arg,  # comment
     ):
         pass
 ```

crates/ruff_python_formatter/tests/snapshots/format@statement__match.py.snap

@@ -464,6 +464,15 @@ match pattern_match_class:
         # e
     ):
         pass
+
+    case A(
+        # a
+        b # b
+        = # c
+        2 # d
+        # e
+    ):
+        pass
 ```
 
 ## Output
@@ -903,10 +912,8 @@ match pattern_match_class:
     ):
         ...
 
-    case Point2D(
-        # end of line
-        0,
-        0,
+    case Point2D(  # end of line
+        0, 0
     ):
         ...
 
@@ -932,8 +939,7 @@ match pattern_match_class:
     case Bar(0, a=None, b="hello"):
         ...
 
-    case FooBar(
-        # leading
+    case FooBar(  # leading
         # leading
         # leading
         # leading
@@ -951,6 +957,15 @@ match pattern_match_class:
         # e
     ):
         pass
+
+    case A(
+        # a
+        b=# b
+        # c
+        2  # d
+        # e
+    ):
+        pass
 ```