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/binhex.pyi

@@ -0,0 +1,42 @@
+from typing import IO, Any, Tuple, Union
+
+class Error(Exception): ...
+
+REASONABLY_LARGE: int
+LINELEN: int
+RUNCHAR: bytes
+
+class FInfo:
+    def __init__(self) -> None: ...
+    Type: str
+    Creator: str
+    Flags: int
+
+_FileInfoTuple = Tuple[str, FInfo, int, int]
+_FileHandleUnion = Union[str, IO[bytes]]
+
+def getfileinfo(name: str) -> _FileInfoTuple: ...
+
+class openrsrc:
+    def __init__(self, *args: Any) -> None: ...
+    def read(self, *args: Any) -> bytes: ...
+    def write(self, *args: Any) -> None: ...
+    def close(self) -> None: ...
+
+class BinHex:
+    def __init__(self, name_finfo_dlen_rlen: _FileInfoTuple, ofp: _FileHandleUnion) -> None: ...
+    def write(self, data: bytes) -> None: ...
+    def close_data(self) -> None: ...
+    def write_rsrc(self, data: bytes) -> None: ...
+    def close(self) -> None: ...
+
+def binhex(inp: str, out: str) -> None: ...
+
+class HexBin:
+    def __init__(self, ifp: _FileHandleUnion) -> None: ...
+    def read(self, *n: int) -> bytes: ...
+    def close_data(self) -> None: ...
+    def read_rsrc(self, *n: int) -> bytes: ...
+    def close(self) -> None: ...
+
+def hexbin(inp: str, out: str) -> None: ...