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/cProfile.pyi

@@ -0,0 +1,33 @@
+import sys
+from _typeshed import AnyPath
+from types import CodeType
+from typing import Any, Callable, Dict, Optional, Tuple, TypeVar, Union
+
+def run(statement: str, filename: Optional[str] = ..., sort: Union[str, int] = ...) -> None: ...
+def runctx(
+    statement: str, globals: Dict[str, Any], locals: Dict[str, Any], filename: Optional[str] = ..., sort: Union[str, int] = ...
+) -> None: ...
+
+_SelfT = TypeVar("_SelfT", bound=Profile)
+_T = TypeVar("_T")
+_Label = Tuple[str, int, str]
+
+class Profile:
+    stats: dict[_Label, tuple[int, int, int, int, dict[_Label, tuple[int, int, int, int]]]]  # undocumented
+    def __init__(
+        self, timer: Callable[[], float] = ..., timeunit: float = ..., subcalls: bool = ..., builtins: bool = ...
+    ) -> None: ...
+    def enable(self) -> None: ...
+    def disable(self) -> None: ...
+    def print_stats(self, sort: Union[str, int] = ...) -> None: ...
+    def dump_stats(self, file: AnyPath) -> None: ...
+    def create_stats(self) -> None: ...
+    def snapshot_stats(self) -> None: ...
+    def run(self: _SelfT, cmd: str) -> _SelfT: ...
+    def runctx(self: _SelfT, cmd: str, globals: Dict[str, Any], locals: Dict[str, Any]) -> _SelfT: ...
+    def runcall(self, __func: Callable[..., _T], *args: Any, **kw: Any) -> _T: ...
+    if sys.version_info >= (3, 8):
+        def __enter__(self: _SelfT) -> _SelfT: ...
+        def __exit__(self, *exc_info: Any) -> None: ...
+
+def label(code: Union[str, CodeType]) -> _Label: ...  # undocumented