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/locale.pyi

@@ -0,0 +1,111 @@
+import sys
+from decimal import Decimal
+from typing import Any, Callable, Dict, Iterable, List, Mapping, Optional, Sequence, Tuple, Union
+
+# workaround for mypy#2010
+if sys.version_info >= (3, 0):
+    from builtins import str as _str
+else:
+    from __builtin__ import str as _str
+
+CODESET: int
+D_T_FMT: int
+D_FMT: int
+T_FMT: int
+T_FMT_AMPM: int
+
+DAY_1: int
+DAY_2: int
+DAY_3: int
+DAY_4: int
+DAY_5: int
+DAY_6: int
+DAY_7: int
+ABDAY_1: int
+ABDAY_2: int
+ABDAY_3: int
+ABDAY_4: int
+ABDAY_5: int
+ABDAY_6: int
+ABDAY_7: int
+
+MON_1: int
+MON_2: int
+MON_3: int
+MON_4: int
+MON_5: int
+MON_6: int
+MON_7: int
+MON_8: int
+MON_9: int
+MON_10: int
+MON_11: int
+MON_12: int
+ABMON_1: int
+ABMON_2: int
+ABMON_3: int
+ABMON_4: int
+ABMON_5: int
+ABMON_6: int
+ABMON_7: int
+ABMON_8: int
+ABMON_9: int
+ABMON_10: int
+ABMON_11: int
+ABMON_12: int
+
+RADIXCHAR: int
+THOUSEP: int
+YESEXPR: int
+NOEXPR: int
+CRNCYSTR: int
+
+ERA: int
+ERA_D_T_FMT: int
+ERA_D_FMT: int
+ERA_T_FMT: int
+
+ALT_DIGITS: int
+
+LC_CTYPE: int
+LC_COLLATE: int
+LC_TIME: int
+LC_MONETARY: int
+LC_MESSAGES: int
+LC_NUMERIC: int
+LC_ALL: int
+
+CHAR_MAX: int
+
+class Error(Exception): ...
+
+def setlocale(category: int, locale: Union[_str, Iterable[_str], None] = ...) -> _str: ...
+def localeconv() -> Mapping[_str, Union[int, _str, List[int]]]: ...
+def nl_langinfo(__key: int) -> _str: ...
+def getdefaultlocale(envvars: Tuple[_str, ...] = ...) -> Tuple[Optional[_str], Optional[_str]]: ...
+def getlocale(category: int = ...) -> Sequence[_str]: ...
+def getpreferredencoding(do_setlocale: bool = ...) -> _str: ...
+def normalize(localename: _str) -> _str: ...
+def resetlocale(category: int = ...) -> None: ...
+def strcoll(string1: _str, string2: _str) -> int: ...
+def strxfrm(string: _str) -> _str: ...
+def format(percent: _str, value: Union[float, Decimal], grouping: bool = ..., monetary: bool = ..., *additional: Any) -> _str: ...
+
+if sys.version_info >= (3, 7):
+    def format_string(f: _str, val: Any, grouping: bool = ..., monetary: bool = ...) -> _str: ...
+
+else:
+    def format_string(f: _str, val: Any, grouping: bool = ...) -> _str: ...
+
+def currency(val: Union[int, float, Decimal], symbol: bool = ..., grouping: bool = ..., international: bool = ...) -> _str: ...
+
+if sys.version_info >= (3, 5):
+    def delocalize(string: _str) -> _str: ...
+
+def atof(string: _str, func: Callable[[_str], float] = ...) -> float: ...
+def atoi(string: _str) -> int: ...
+def str(val: float) -> _str: ...
+
+locale_alias: Dict[_str, _str]  # undocumented
+locale_encoding_alias: Dict[_str, _str]  # undocumented
+windows_locale: Dict[int, _str]  # undocumented