Add macurl2path stub (#3785)

* Add macurl2path stub, types based on urllib

* Fix types, remove undocumented

The whole module is undocumented, no reason to just mention it on one call

* Module was removed in 3.7, stubtest shouldn't care about it

* Module was removed in 3.7, stubtest shouldn't care about it

stdlib/3/macurl2path.pyi

@@ -0,0 +1,9 @@
+
+import sys
+
+from typing import Union
+
+if sys.version_info < (3, 7):
+    def url2pathname(pathname: str) -> str: ...
+    def pathname2url(pathname: str) -> str: ...
+    def _pncomp2url(component: Union[str, bytes]) -> str: ...