Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/_thread.pyi

@@ -0,0 +1,41 @@
+import sys
+from threading import Thread
+from types import TracebackType
+from typing import Any, Callable, Dict, NoReturn, Optional, Tuple, Type
+
+error = RuntimeError
+
+def _count() -> int: ...
+
+_dangling: Any
+
+class LockType:
+    def acquire(self, blocking: bool = ..., timeout: float = ...) -> bool: ...
+    def release(self) -> None: ...
+    def locked(self) -> bool: ...
+    def __enter__(self) -> bool: ...
+    def __exit__(
+        self, type: Optional[Type[BaseException]], value: Optional[BaseException], traceback: Optional[TracebackType]
+    ) -> None: ...
+
+def start_new_thread(function: Callable[..., Any], args: Tuple[Any, ...], kwargs: Dict[str, Any] = ...) -> int: ...
+def interrupt_main() -> None: ...
+def exit() -> NoReturn: ...
+def allocate_lock() -> LockType: ...
+def get_ident() -> int: ...
+def stack_size(size: int = ...) -> int: ...
+
+TIMEOUT_MAX: float
+
+if sys.version_info >= (3, 8):
+    def get_native_id() -> int: ...  # only available on some platforms
+    class _ExceptHookArgs(Tuple[Type[BaseException], Optional[BaseException], Optional[TracebackType], Optional[Thread]]):
+        @property
+        def exc_type(self) -> Type[BaseException]: ...
+        @property
+        def exc_value(self) -> Optional[BaseException]: ...
+        @property
+        def exc_traceback(self) -> Optional[TracebackType]: ...
+        @property
+        def thread(self) -> Optional[Thread]: ...
+    _excepthook: Callable[[_ExceptHookArgs], Any]