Patch panics for stringified annotations for now

Author: sharkdp

crates/ty_python_semantic/resources/mdtest/implicit_type_aliases.md

@@ -558,6 +558,23 @@ def _(
     reveal_type(list_of_ints2)  # revealed: list[int]
 ```
 
+### In stringified annotations
+
+Generic implicit type aliases can be specialized in stringified annotations:
+
+```py
+from typing_extensions import TypeVar
+
+T = TypeVar("T")
+
+MyList = list[T]
+
+def _(
+    list_of_ints: "MyList[int]",
+):
+    reveal_type(list_of_ints)  # revealed: @Todo(Specialization of generic type alias in stringified annotation)
+```
+
 ### Error cases
 
 A generic alias that is already fully specialized cannot be specialized again:

crates/ty_python_semantic/src/types/infer/builder/type_expression.rs

@@ -723,6 +723,14 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
     ) -> Type<'db> {
         let db = self.db();
 
+        if self
+            .index
+            .try_expression_scope_id(&ast::ExprRef::from(subscript))
+            .is_none()
+        {
+            return todo_type!("Specialization of generic type alias in stringified annotation");
+        }
+
         let definitions = match &*subscript.value {
             ast::Expr::Name(id) => {
                 // TODO: This is an expensive call to an API that was never meant to be called from