[red-knot] Remove match pattern definition visitor (#13209)

## Summary

This PR is based on this discussion:
https://github.com/astral-sh/ruff/pull/13147#discussion_r1739408653.

**Todo**

- [x] Add documentation for `MatchPatternState`

## Test Plan

`cargo insta test` and `cargo clippy`

crates/red_knot_python_semantic/src/semantic_index.rs

@@ -1097,16 +1097,62 @@ match subject:
         );
 
         let use_def = use_def_map(&db, global_scope_id);
-        for name in ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l"] {
+        for (name, expected_index) in [
+            ("a", 0),
+            ("b", 0),
+            ("c", 1),
+            ("d", 2),
+            ("e", 0),
+            ("f", 1),
+            ("g", 0),
+            ("h", 1),
+            ("i", 0),
+            ("j", 1),
+            ("k", 0),
+            ("l", 1),
+        ] {
             let definition = use_def
                 .first_public_definition(
                     global_table.symbol_id_by_name(name).expect("symbol exists"),
                 )
                 .expect("Expected with item definition for {name}");
-            assert!(matches!(
-                definition.node(&db),
-                DefinitionKind::MatchPattern(_)
-            ));
+            if let DefinitionKind::MatchPattern(pattern) = definition.node(&db) {
+                assert_eq!(pattern.index(), expected_index);
+            } else {
+                panic!("Expected match pattern definition for {name}");
+            }
+        }
+    }
+
+    #[test]
+    fn nested_match_case() {
+        let TestCase { db, file } = test_case(
+            "
+match 1:
+    case first:
+        match 2:
+            case second:
+                pass
+",
+        );
+
+        let global_scope_id = global_scope(&db, file);
+        let global_table = symbol_table(&db, global_scope_id);
+
+        assert_eq!(names(&global_table), vec!["first", "second"]);
+
+        let use_def = use_def_map(&db, global_scope_id);
+        for (name, expected_index) in [("first", 0), ("second", 0)] {
+            let definition = use_def
+                .first_public_definition(
+                    global_table.symbol_id_by_name(name).expect("symbol exists"),
+                )
+                .expect("Expected with item definition for {name}");
+            if let DefinitionKind::MatchPattern(pattern) = definition.node(&db) {
+                assert_eq!(pattern.index(), expected_index);
+            } else {
+                panic!("Expected match pattern definition for {name}");
+            }
         }
     }