Split stdlib into Python 2 and 3 versions (#5442)

All new files in stdlib/@python2 are straight copies of the
corresponding files in stdlib.

stdlib/@python2/fileinput.pyi

@@ -0,0 +1,78 @@
+import sys
+from _typeshed import AnyPath
+from typing import IO, Any, AnyStr, Callable, Generic, Iterable, Iterator, Optional, Union
+
+if sys.version_info >= (3, 8):
+    def input(
+        files: Union[AnyPath, Iterable[AnyPath], None] = ...,
+        inplace: bool = ...,
+        backup: str = ...,
+        *,
+        mode: str = ...,
+        openhook: Callable[[AnyPath, str], IO[AnyStr]] = ...,
+    ) -> FileInput[AnyStr]: ...
+
+else:
+    def input(
+        files: Union[AnyPath, Iterable[AnyPath], None] = ...,
+        inplace: bool = ...,
+        backup: str = ...,
+        bufsize: int = ...,
+        mode: str = ...,
+        openhook: Callable[[AnyPath, str], IO[AnyStr]] = ...,
+    ) -> FileInput[AnyStr]: ...
+
+def close() -> None: ...
+def nextfile() -> None: ...
+def filename() -> str: ...
+def lineno() -> int: ...
+def filelineno() -> int: ...
+def fileno() -> int: ...
+def isfirstline() -> bool: ...
+def isstdin() -> bool: ...
+
+class FileInput(Iterable[AnyStr], Generic[AnyStr]):
+    if sys.version_info >= (3, 8):
+        def __init__(
+            self,
+            files: Union[None, AnyPath, Iterable[AnyPath]] = ...,
+            inplace: bool = ...,
+            backup: str = ...,
+            *,
+            mode: str = ...,
+            openhook: Callable[[AnyPath, str], IO[AnyStr]] = ...,
+        ) -> None: ...
+    else:
+        def __init__(
+            self,
+            files: Union[None, AnyPath, Iterable[AnyPath]] = ...,
+            inplace: bool = ...,
+            backup: str = ...,
+            bufsize: int = ...,
+            mode: str = ...,
+            openhook: Callable[[AnyPath, str], IO[AnyStr]] = ...,
+        ) -> None: ...
+    def __del__(self) -> None: ...
+    def close(self) -> None: ...
+    if sys.version_info >= (3, 2):
+        def __enter__(self) -> FileInput[AnyStr]: ...
+        def __exit__(self, type: Any, value: Any, traceback: Any) -> None: ...
+    def __iter__(self) -> Iterator[AnyStr]: ...
+    def __next__(self) -> AnyStr: ...
+    def __getitem__(self, i: int) -> AnyStr: ...
+    def nextfile(self) -> None: ...
+    def readline(self) -> AnyStr: ...
+    def filename(self) -> str: ...
+    def lineno(self) -> int: ...
+    def filelineno(self) -> int: ...
+    def fileno(self) -> int: ...
+    def isfirstline(self) -> bool: ...
+    def isstdin(self) -> bool: ...
+
+def hook_compressed(filename: AnyPath, mode: str) -> IO[Any]: ...
+
+if sys.version_info >= (3, 6):
+    def hook_encoded(encoding: str, errors: Optional[str] = ...) -> Callable[[AnyPath, str], IO[Any]]: ...
+
+else:
+    def hook_encoded(encoding: str) -> Callable[[AnyPath, str], IO[Any]]: ...