Handle PEP 613 aliases as well

Author: sharkdp

crates/ty_python_semantic/resources/mdtest/pep613_type_aliases.md

@@ -96,6 +96,24 @@ def _(x: MyAlias):
     reveal_type(x)  # revealed: int | ((str, /) -> int)
 ```
 
+## Generic aliases
+
+```py
+from typing import TypeAlias, TypeVar
+
+T = TypeVar("T")
+
+MyList: TypeAlias = list[T]
+ListOrSet: TypeAlias = list[T] | set[T]
+
+reveal_type(MyList)  # revealed: <class 'list[T]'>
+reveal_type(ListOrSet)  # revealed: types.UnionType
+
+def _(list_of_int: MyList[int], list_or_set_of_str: ListOrSet[str]):
+    reveal_type(list_of_int)  # revealed: list[int]
+    reveal_type(list_or_set_of_str)  # revealed: list[str] | set[str]
+```
+
 ## Subscripted generic alias in union
 
 ```py

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

@@ -5531,11 +5531,16 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                 self.deferred_state = DeferredExpressionState::Deferred;
             }
 
+            let previous_typevar_binding_context = self.typevar_binding_context;
+            self.typevar_binding_context = Some(definition);
+
             let inferred_ty = self.infer_maybe_standalone_expression(
                 value,
                 TypeContext::new(Some(declared.inner_type())),
             );
 
+            self.typevar_binding_context = previous_typevar_binding_context;
+
             self.deferred_state = previous_deferred_state;
 
             self.dataclass_field_specifiers.clear();