[ty] Disallow typing.TypedDict in type expressions (#19777)

## Summary

Disallow `typing.TypedDict` in type expressions.

Related reference: https://github.com/python/mypy/issues/11030

## Test Plan

New Markdown tests, checked ecosystem and conformance test impact.

crates/ty_python_semantic/resources/mdtest/typed_dict.md

@@ -375,6 +375,17 @@ reveal_type(Message.__required_keys__)  # revealed: @Todo(Support for `TypedDict
 msg.content
 ```
 
+## Error cases
+
+### `typing.TypedDict` is not allowed in type expressions
+
+```py
+from typing import TypedDict
+
+# error: [invalid-type-form] "The special form `typing.TypedDict` is not allowed in type expressions."
+x: TypedDict = {"name": "Alice"}
+```
+
 ## Diagnostics
 
 <!-- snapshot-diagnostics -->

crates/ty_python_semantic/src/types.rs

@@ -5414,7 +5414,12 @@ impl<'db> Type<'db> {
                     )))
                 }
                 SpecialFormType::TypeAlias => Ok(Type::Dynamic(DynamicType::TodoTypeAlias)),
-                SpecialFormType::TypedDict => Ok(todo_type!("Support for `typing.TypedDict`")),
+                SpecialFormType::TypedDict => Err(InvalidTypeExpressionError {
+                    invalid_expressions: smallvec::smallvec_inline![
+                        InvalidTypeExpression::TypedDict
+                    ],
+                    fallback_type: Type::unknown(),
+                }),
 
                 SpecialFormType::Literal
                 | SpecialFormType::Union
@@ -6560,6 +6565,8 @@ enum InvalidTypeExpression<'db> {
     Deprecated,
     /// Same for `dataclasses.Field`
     Field,
+    /// Same for `typing.TypedDict`
+    TypedDict,
     /// Type qualifiers are always invalid in *type expressions*,
     /// but these ones are okay with 0 arguments in *annotation expressions*
     TypeQualifier(SpecialFormType),
@@ -6607,6 +6614,11 @@ impl<'db> InvalidTypeExpression<'db> {
                     InvalidTypeExpression::Field => {
                         f.write_str("`dataclasses.Field` is not allowed in type expressions")
                     }
+                    InvalidTypeExpression::TypedDict => {
+                        f.write_str(
+                            "The special form `typing.TypedDict` is not allowed in type expressions. \
+                            Did you mean to use a concrete TypedDict or `collections.abc.Mapping[str, object]` instead?")
+                    }
                     InvalidTypeExpression::TypeQualifier(qualifier) => write!(
                         f,
                         "Type qualifier `{qualifier}` is not allowed in type expressions \

crates/ty_python_semantic/src/types/class.rs

@@ -2316,7 +2316,9 @@ impl<'db> ClassLiteral<'db> {
                     }
                 }
                 ClassBase::TypedDict => {
-                    return Place::bound(todo_type!("Support for `TypedDict`")).into();
+                    return KnownClass::TypedDictFallback
+                        .to_instance(db)
+                        .instance_member(db, name);
                 }
             }
         }