Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/distutils/extension.pyi

@@ -0,0 +1,22 @@
+from typing import List, Optional, Tuple
+
+class Extension:
+    def __init__(
+        self,
+        name: str,
+        sources: List[str],
+        include_dirs: List[str] = ...,
+        define_macros: List[Tuple[str, Optional[str]]] = ...,
+        undef_macros: List[str] = ...,
+        library_dirs: List[str] = ...,
+        libraries: List[str] = ...,
+        runtime_library_dirs: List[str] = ...,
+        extra_objects: List[str] = ...,
+        extra_compile_args: List[str] = ...,
+        extra_link_args: List[str] = ...,
+        export_symbols: List[str] = ...,
+        swig_opts: Optional[str] = ...,  # undocumented
+        depends: List[str] = ...,
+        language: str = ...,
+        optional: bool = ...,
+    ) -> None: ...