bpo-35555: IDLE: Gray out Code Context menu item on non-editors (#11282)

The Code Context menu item only works on Editor windows so disable it for others.
diff --git a/Lib/idlelib/NEWS.txt b/Lib/idlelib/NEWS.txt
index f46a2d7..6886289 100644
--- a/Lib/idlelib/NEWS.txt
+++ b/Lib/idlelib/NEWS.txt
@@ -3,6 +3,8 @@
 ======================================
 
 
+bpo-35555: Gray out Code Context menu entry when it's not applicable.
+
 bpo-22703: Improve the Code Context and Zoom Height menu labels.
 The Code Context menu label now toggles between Show/Hide Code Context.
 The Zoom Height menu now toggles between Zoom/Restore Height.