Unify file descriptor definitions (#3584)

The _types module can house any common type defintions used throughout
the rest of typeshed to keep defintions in sync.

First candidate is file descriptors where anything with `fileno()`
method is accepted. There were several different implementations in
various files that can be unified.

stdlib/3/fcntl.pyi

@@ -1,6 +1,7 @@
 # Stubs for fcntl
 from io import IOBase
 from typing import Any, IO, Union
+from _types import FileDescriptorLike
 
 FASYNC: int
 FD_CLOEXEC: int
@@ -75,21 +76,19 @@ LOCK_SH: int
 LOCK_UN: int
 LOCK_WRITE: int
 
-_AnyFile = Union[int, IO[Any], IOBase]
-
 # TODO All these return either int or bytes depending on the value of
 # cmd (not on the type of arg).
-def fcntl(fd: _AnyFile,
+def fcntl(fd: FileDescriptorLike,
           cmd: int,
           arg: Union[int, bytes] = ...) -> Any: ...
 # TODO This function accepts any object supporting a buffer interface,
 # as arg, is there a better way to express this than bytes?
-def ioctl(fd: _AnyFile,
+def ioctl(fd: FileDescriptorLike,
           request: int,
           arg: Union[int, bytes] = ...,
           mutate_flag: bool = ...) -> Any: ...
-def flock(fd: _AnyFile, operation: int) -> None: ...
-def lockf(fd: _AnyFile,
+def flock(fd: FileDescriptorLike, operation: int) -> None: ...
+def lockf(fd: FileDescriptorLike,
           cmd: int,
           len: int = ...,
           start: int = ...,