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/turtledemo/__main__.py

@@ -89,9 +89,9 @@ import sys
 import os
 
 from tkinter import *
-from idlelib.Percolator import Percolator
-from idlelib.ColorDelegator import ColorDelegator
-from idlelib.textView import view_text
+from idlelib.percolator import Percolator
+from idlelib.colorizer import ColorDelegator
+from idlelib.textview import view_text
 from turtledemo import __doc__ as about_turtledemo
 
 import turtle