Annotations for remaining Python 3.8 additions (#3358)

* Add os.add_dll_directory()
* Add memfd_create() and flags
* Add type annotation to flags
* Add stat_result.st_reparse_tag and flags
* Add ncurses_version
* Add Path.link_to()
* Add Picker.reducer_override()
* Add plistlib.UID
* Add has_dualstack_ipv6() and create_server()
* Add shlex.join()
* Add SSL methods and fields
* Add Python 3.8 statistics functions and classes
* Remove obsolete sys.subversion
* Add sys.unraisablehook
* Add threading.excepthook
* Add get_native_id() and Thread.native_id
* Add Python 3.8 tkinter methods
* Add CLOCK_UPTIME_RAW
* Add SupportsIndex
* Add typing.get_origin() and get_args()
* Add unicodedata.is_normalized
* Add unittest.mock.AsyncMock

Currently this is just an alias for Any like Mock and MagicMock. All of
these classes should probably be sub-classing Any and add their own
methods. See also #3224.

* Add unittest cleanup methods
* Add IsolatedAsyncioTestCase
* Add ElementTree.canonicalize() and C14NWriterTarget
* cProfile.Profile can be used as a context manager
* Add asyncio task name handling
* mmap.flush() now always returns None
* Add posonlyargcount to CodeType

stdlib/3/stat.pyi

@@ -17,58 +17,81 @@ def S_IFMT(mode: int) -> int: ...
 
 def filemode(mode: int) -> str: ...
 
-ST_MODE = 0
-ST_INO = 0
-ST_DEV = 0
-ST_NLINK = 0
-ST_UID = 0
-ST_GID = 0
-ST_SIZE = 0
-ST_ATIME = 0
-ST_MTIME = 0
-ST_CTIME = 0
+ST_MODE: int
+ST_INO: int
+ST_DEV: int
+ST_NLINK: int
+ST_UID: int
+ST_GID: int
+ST_SIZE: int
+ST_ATIME: int
+ST_MTIME: int
+ST_CTIME: int
 
-S_IFSOCK = 0
-S_IFLNK = 0
-S_IFREG = 0
-S_IFBLK = 0
-S_IFDIR = 0
-S_IFCHR = 0
-S_IFIFO = 0
-S_ISUID = 0
-S_ISGID = 0
-S_ISVTX = 0
+S_IFSOCK: int
+S_IFLNK: int
+S_IFREG: int
+S_IFBLK: int
+S_IFDIR: int
+S_IFCHR: int
+S_IFIFO: int
+S_ISUID: int
+S_ISGID: int
+S_ISVTX: int
 
-S_IRWXU = 0
-S_IRUSR = 0
-S_IWUSR = 0
-S_IXUSR = 0
+S_IRWXU: int
+S_IRUSR: int
+S_IWUSR: int
+S_IXUSR: int
 
-S_IRWXG = 0
-S_IRGRP = 0
-S_IWGRP = 0
-S_IXGRP = 0
+S_IRWXG: int
+S_IRGRP: int
+S_IWGRP: int
+S_IXGRP: int
 
-S_IRWXO = 0
-S_IROTH = 0
-S_IWOTH = 0
-S_IXOTH = 0
+S_IRWXO: int
+S_IROTH: int
+S_IWOTH: int
+S_IXOTH: int
 
-S_ENFMT = 0
-S_IREAD = 0
-S_IWRITE = 0
-S_IEXEC = 0
+S_ENFMT: int
+S_IREAD: int
+S_IWRITE: int
+S_IEXEC: int
 
-UF_NODUMP = 0
-UF_IMMUTABLE = 0
-UF_APPEND = 0
-UF_OPAQUE = 0
-UF_NOUNLINK = 0
+UF_NODUMP: int
+UF_IMMUTABLE: int
+UF_APPEND: int
+UF_OPAQUE: int
+UF_NOUNLINK: int
 if sys.platform == 'darwin':
-    UF_COMPRESSED = 0  # OS X 10.6+ only
-    UF_HIDDEN = 0     # OX X 10.5+ only
-SF_ARCHIVED = 0
-SF_IMMUTABLE = 0
-SF_APPEND = 0
-SF_NOUNLINK = 0
-SF_SNAPSHOT = 0
+    UF_COMPRESSED: int  # OS X 10.6+ only
+    UF_HIDDEN: int     # OX X 10.5+ only
+SF_ARCHIVED: int
+SF_IMMUTABLE: int
+SF_APPEND: int
+SF_NOUNLINK: int
+SF_SNAPSHOT: int
+
+FILE_ATTRIBUTE_ARCHIVE: int
+FILE_ATTRIBUTE_COMPRESSED: int
+FILE_ATTRIBUTE_DEVICE: int
+FILE_ATTRIBUTE_DIRECTORY: int
+FILE_ATTRIBUTE_ENCRYPTED: int
+FILE_ATTRIBUTE_HIDDEN: int
+FILE_ATTRIBUTE_INTEGRITY_STREAM: int
+FILE_ATTRIBUTE_NORMAL: int
+FILE_ATTRIBUTE_NOT_CONTENT_INDEXED: int
+FILE_ATTRIBUTE_NO_SCRUB_DATA: int
+FILE_ATTRIBUTE_OFFLINE: int
+FILE_ATTRIBUTE_READONLY: int
+FILE_ATTRIBUTE_REPARSE_POINT: int
+FILE_ATTRIBUTE_SPARSE_FILE: int
+FILE_ATTRIBUTE_SYSTEM: int
+FILE_ATTRIBUTE_TEMPORARY: int
+FILE_ATTRIBUTE_VIRTUAL: int
+
+if sys.platform == "win32" and sys.version_info >= (3, 8):
+    IO_REPARSE_TAG_SYMLINK: int
+    IO_REPARSE_TAG_MOUNT_POINT: int
+    IO_REPARSE_TAG_APPEXECLINK: int