Add Shadow.pyi from typeshed's pull request

Cython/Shadow.pyi

+from builtins import (int as py_int, float as py_float,
+                      bool as py_bool, str as py_str)
+from typing import (Union, Dict, Any, Sequence, Optional,
+                    List, TypeVar, Type, Generic)
+
+int = py_int
+long = py_int
+longlong = py_int
+short = py_int
+char = py_int
+sint = py_int
+slong = py_int
+slonglong = py_int
+sshort = py_int
+schar = py_int
+uint = py_int
+ulong = py_int
+ulonglong = py_int
+ushort = py_int
+uchar = py_int
+size_t = py_int
+Py_ssize_t = py_int
+float = py_float
+double = py_float
+longdouble = py_float
+bint = py_bool
+void = Union[None]
+basestring = py_str
+
+gs: Dict[str, Any]  # Should match the return type of globals()
+
+_T = TypeVar('_T')
+
+class _ArrayType(object, Generic[_T]):
+    is_array: bool
+    subtypes: Sequence[str]
+    dtype: _T
+    ndim: int
+    is_c_contig: bool
+    is_f_contig: bool
+    inner_contig: bool
+    broadcasting: Any
+
+    # broadcasting is not used, so it's not clear about its type
+    def __init__(self, dtype: _T, ndim: int, is_c_contig: bool = ...,
+                 is_f_contig: bool = ..., inner_contig: bool = ...,
+                 broadcasting: Any = ...) -> None: ...
+    def __repr__(self) -> str: ...
+
+class CythonTypeObject(object):
+    ...
+
+class CythonType(CythonTypeObject):
+    ...
+
+class PointerType(CythonType, Generic[_T]):
+    def __init__(
+        self,
+        value: Optional[Union[ArrayType[_T],
+                              PointerType[_T], List[_T], int]] = ...
+    ) -> None: ...
+    def __getitem__(self, ix: int) -> _T: ...
+    def __setitem__(self, ix: int, value: _T) -> None: ...
+    def __eq__(self, value: object) -> bool: ...
+    def __repr__(self) -> str: ...
+
+class ArrayType(PointerType[_T]):
+    def __init__(self) -> None: ...
+
+def index_type(
+    base_type: _T, item: Union[tuple, slice, int]) -> _ArrayType[_T]: ...
+
+def pointer(basetype: _T) -> Type[PointerType[_T]]: ...
+
+def array(basetype: _T, n: int) -> Type[ArrayType[_T]]: ...
+
+class typedef(CythonType, Generic[_T]):
+    name: str
+
+    def __init__(self, type: _T, name: Optional[str] = ...) -> None: ...
+    def __call__(self, *arg: Any) -> _T: ...
+    def __repr__(self) -> str: ...
+    __getitem__ = index_type