Make os.fchdir, os.fsync, and os.fdatasync accept FileDescriptorLike (#4544)

For the fd passed to these functions, CPython accepts not just an int,
but also anything with a fileno() method.

Fixes #4539

stdlib/2/posix.pyi

@@ -1,3 +1,4 @@
+from _typeshed import FileDescriptorLike
 from typing import IO, AnyStr, Dict, List, Mapping, NamedTuple, Optional, Sequence, Tuple, TypeVar, Union
 
 error = OSError
@@ -105,17 +106,17 @@ def dup(fd: int) -> int: ...
 def dup2(fd: int, fd2: int) -> None: ...
 def execv(path: str, args: Sequence[str], env: Mapping[str, str]) -> None: ...
 def execve(path: str, args: Sequence[str], env: Mapping[str, str]) -> None: ...
-def fchdir(fd: int) -> None: ...
+def fchdir(fd: FileDescriptorLike) -> None: ...
 def fchmod(fd: int, mode: int) -> None: ...
 def fchown(fd: int, uid: int, gid: int) -> None: ...
-def fdatasync(fd: int) -> None: ...
+def fdatasync(fd: FileDescriptorLike) -> None: ...
 def fdopen(fd: int, mode: str = ..., bufsize: int = ...) -> IO[str]: ...
 def fork() -> int: ...
 def forkpty() -> Tuple[int, int]: ...
 def fpathconf(fd: int, name: str) -> None: ...
 def fstat(fd: int) -> stat_result: ...
 def fstatvfs(fd: int) -> statvfs_result: ...
-def fsync(fd: int) -> None: ...
+def fsync(fd: FileDescriptorLike) -> None: ...
 def ftruncate(fd: int, length: int) -> None: ...
 def getcwd() -> str: ...
 def getcwdu() -> unicode: ...