Add various missing undocumented functions (#4554)

Mostly addresses #2149

stdlib/2and3/pickle.pyi

@@ -1,10 +1,12 @@
 import sys
-from typing import IO, Any, Callable, Iterable, Iterator, Mapping, Optional, Tuple, Union
+from typing import IO, Any, Callable, Iterable, Iterator, Mapping, Optional, Tuple, Type, Union
 
 HIGHEST_PROTOCOL: int
 if sys.version_info >= (3, 0):
     DEFAULT_PROTOCOL: int
 
+bytes_types: Tuple[Type[Any], ...]  # undocumented
+
 if sys.version_info >= (3, 8):
     # TODO: holistic design for buffer interface (typing.Buffer?)
     class PickleBuffer:
@@ -179,3 +181,6 @@ if sys.version_info >= (3, 4):
     STACK_GLOBAL: bytes
     MEMOIZE: bytes
     FRAME: bytes
+
+def encode_long(x: int) -> bytes: ...  # undocumented
+def decode_long(data: bytes) -> int: ...  # undocumented

stdlib/2and3/pkgutil.pyi

@@ -1,6 +1,5 @@
-# Stubs for pkgutil
-
 import sys
+from _typeshed import SupportsRead
 from typing import IO, Any, Callable, Iterable, Iterator, NamedTuple, Optional, Tuple, Union
 
 if sys.version_info >= (3,):
@@ -32,6 +31,7 @@ def get_importer(path_item: str) -> Optional[PathEntryFinder]: ...
 def get_loader(module_or_name: str) -> Loader: ...
 def iter_importers(fullname: str = ...) -> Iterator[Union[MetaPathFinder, PathEntryFinder]]: ...
 def iter_modules(path: Optional[Iterable[str]] = ..., prefix: str = ...) -> Iterator[_ModuleInfoLike]: ...
+def read_code(stream: SupportsRead[bytes]) -> Any: ...  # undocumented
 def walk_packages(
     path: Optional[Iterable[str]] = ..., prefix: str = ..., onerror: Optional[Callable[[str], None]] = ...
 ) -> Iterator[_ModuleInfoLike]: ...

stdlib/2and3/sre_compile.pyi

@@ -2,9 +2,25 @@
 # and https://github.com/python/cpython/blob/master/Lib/sre_compile.py
 
 import sys
+from sre_constants import (
+    SRE_FLAG_DEBUG as SRE_FLAG_DEBUG,
+    SRE_FLAG_DOTALL as SRE_FLAG_DOTALL,
+    SRE_FLAG_IGNORECASE as SRE_FLAG_IGNORECASE,
+    SRE_FLAG_LOCALE as SRE_FLAG_LOCALE,
+    SRE_FLAG_MULTILINE as SRE_FLAG_MULTILINE,
+    SRE_FLAG_TEMPLATE as SRE_FLAG_TEMPLATE,
+    SRE_FLAG_UNICODE as SRE_FLAG_UNICODE,
+    SRE_FLAG_VERBOSE as SRE_FLAG_VERBOSE,
+    SRE_INFO_CHARSET as SRE_INFO_CHARSET,
+    SRE_INFO_LITERAL as SRE_INFO_LITERAL,
+    SRE_INFO_PREFIX as SRE_INFO_PREFIX,
+)
 from sre_parse import SubPattern
 from typing import Any, List, Pattern, Tuple, Type, Union
 
+if sys.version_info >= (3,):
+    from sre_constants import SRE_FLAG_ASCII as SRE_FLAG_ASCII
+
 MAXCODE: int
 if sys.version_info < (3, 0):
     STRING_TYPES: Tuple[Type[str], Type[unicode]]

stdlib/3/_thread.pyi

@@ -1,5 +1,3 @@
-# Stubs for _thread
-
 import sys
 from threading import Thread
 from types import TracebackType

stdlib/3/urllib/request.pyi

@@ -1,5 +1,3 @@
-# Stubs for urllib.request (Python 3.4)
-
 import os
 import ssl
 import sys