[syntax-errors] Duplicate attributes in match class pattern (#17186)

Summary
--

Detects duplicate attributes in a `match` class pattern:

```python
match x:
    case Class(x=1, x=2): ...
```

which are more analogous to the similar check for mapping patterns than
to the
multiple assignments rule.

I also realized that both this and the mapping check would only work on
top-level patterns, despite the possibility that they can be nested
inside other
patterns:

```python
match x:
    case [{"x": 1, "x": 2}]: ...  # false negative in the old version
```

and moved these checks into the recursive pattern visitor instead.

I also tidied up some of the names like the `multiple_case_assignment`
function
and the `MultipleCaseAssignmentVisitor`, which are now doing more than
checking
for multiple assignments.

Test Plan
--

New inline tests for both classes and mappings.

crates/ruff_python_parser/resources/inline/err/duplicate_match_class_attr.py

@@ -0,0 +1,6 @@
+match x:
+    case Class(x=1, x=2): ...
+    case [Class(x=1, x=2)]: ...
+    case {"x": x, "y": Foo(x=1, x=2)}: ...
+    case [{}, {"x": x, "y": Foo(x=1, x=2)}]: ...
+    case Class(x=1, d={"x": 1, "x": 2}, other=Class(x=1, x=2)): ...

crates/ruff_python_parser/resources/inline/err/duplicate_match_key.py

@@ -17,3 +17,6 @@ match x:
     """: 2}: ...
     case {"x": 1, "x": 2, "x": 3}: ...
     case {0: 1, "x": 1, 0: 2, "x": 2}: ...
+    case [{"x": 1, "x": 2}]: ...
+    case Foo(x=1, y={"x": 1, "x": 2}): ...
+    case [Foo(x=1), Foo(x=1, y={"x": 1, "x": 2})]: ...