bpo-31460: Simplify the API of IDLE's Module Browser. (#3842)

Passing a widget instead of an flist with a root widget opens the option of
creating a browser frame that is only part of a window. Passing a full file
name instead of pieces assumed to come from a .py file opens the possibility
of browsing python files that do not end in .py.

Lib/idlelib/editor.py

@@ -664,10 +664,8 @@ class EditorWindow(object):
             filename = self.open_module()
             if filename is None:
                 return "break"
-        head, tail = os.path.split(filename)
-        base, ext = os.path.splitext(tail)
         from idlelib import browser
-        browser.ModuleBrowser(self.flist, base, [head])
+        browser.ModuleBrowser(self.root, filename)
         return "break"
 
     def open_path_browser(self, event=None):