Issue #24225: Within idlelib files, update idlelib module names.

This follows the previous patch that changed idlelib file names.
Class names that matched old module names are not changed.
Change idlelib imports in turtledemo.__main__.

Exception: config-extensions.def.  Previously, extension section
names, file names, and class names had to match.  Changing section
names would create cross-version conflicts in config-extensions.cfg
(user customizations).  Instead map old names to new file names
at point of import in editor.EditorWindow.load_extension.

Patch extensively tested with test_idle, idle_test.htest.py, a custom
import-all test, running IDLE in a console to catch messages,
and testing each menu item.  Based on a patch by Al Sweigart.

Lib/idlelib/filelist.py

@@ -6,7 +6,7 @@ import tkinter.messagebox as tkMessageBox
 class FileList:
 
     # N.B. this import overridden in PyShellFileList.
-    from idlelib.EditorWindow import EditorWindow
+    from idlelib.editor import EditorWindow
 
     def __init__(self, root):
         self.root = root
@@ -111,7 +111,7 @@ class FileList:
 
 
 def _test():
-    from idlelib.EditorWindow import fixwordbreaks
+    from idlelib.editor import fixwordbreaks
     import sys
     root = Tk()
     fixwordbreaks(root)