bpo-37530: simplify, optimize and clean up IDLE code context (GH-14675)

* Only create CodeContext instances for "real" editors windows, but
  not e.g. shell or output windows.
* Remove configuration update Tk event fired every second, by having
  the editor window ask its code context widget to update when
  necessary, i.e. upon font or highlighting updates.
* When code context isn't being shown, avoid having a Tk event fired
  every 100ms to check whether the code context needs to be updated.
* Use the editor window's getlineno() method where applicable.
* Update font of the code context widget before the main text widget

Lib/idlelib/outwin.py

@@ -74,6 +74,8 @@ class OutputWindow(EditorWindow):
         ("Go to file/line", "<<goto-file-line>>", None),
     ]
 
+    allow_codecontext = False
+
     def __init__(self, *args):
         EditorWindow.__init__(self, *args)
         self.text.bind("<<goto-file-line>>", self.goto_file_line)