Implement support for TypeVar inference for __new__

test/completion/pep0484_generic_parameters.py

@@ -11,6 +11,7 @@ from typing import (
     TypeVar,
     Union,
     Sequence,
+    Self,
 )
 
 K = TypeVar('K')
@@ -395,3 +396,11 @@ def generic_func2(arg: T) -> Union[int, str, T]: pass
 generic_func1(b"hello")
 #? int() str() bytes()
 generic_func2(b"hello")
+
+class CustomGeneric2(Generic[T_co]):
+    val: T_co
+    def __init__(cls, val: T_co) -> Self:
+        raise NotImplementedError
+
+#? int()
+CustomGeneric2(1).val