Re-organize directory structure (#4971)

See discussion in #2491

Co-authored-by: Ivan Levkivskyi <ilevkivskyi@dropbox.com>

stdlib/multiprocessing/process.pyi

@@ -0,0 +1,39 @@
+import sys
+from typing import Any, Callable, List, Mapping, Optional, Tuple
+
+class BaseProcess:
+    name: str
+    daemon: bool
+    authkey: bytes
+    def __init__(
+        self,
+        group: None = ...,
+        target: Optional[Callable[..., Any]] = ...,
+        name: Optional[str] = ...,
+        args: Tuple[Any, ...] = ...,
+        kwargs: Mapping[str, Any] = ...,
+        *,
+        daemon: Optional[bool] = ...,
+    ) -> None: ...
+    def run(self) -> None: ...
+    def start(self) -> None: ...
+    def terminate(self) -> None: ...
+    if sys.version_info >= (3, 7):
+        def kill(self) -> None: ...
+        def close(self) -> None: ...
+    def join(self, timeout: Optional[float] = ...) -> None: ...
+    def is_alive(self) -> bool: ...
+    @property
+    def exitcode(self) -> Optional[int]: ...
+    @property
+    def ident(self) -> Optional[int]: ...
+    @property
+    def pid(self) -> Optional[int]: ...
+    @property
+    def sentinel(self) -> int: ...
+
+def current_process() -> BaseProcess: ...
+def active_children() -> List[BaseProcess]: ...
+
+if sys.version_info >= (3, 8):
+    def parent_process() -> Optional[BaseProcess]: ...