The Window menu never listed the application's windows, because AppKit had none of Cocoa's Windows menu support.
* CPApplication.j: Add windowsMenu, setWindowsMenu:, addWindowsItem:title:filename:, changeWindowsItem:title:filename:, removeWindowsItem:, updateWindowsItem: and arrangeInFront:; find the menu named _CPWindowsMenu in the main menu, and list the visible windows when the main menu is set.
* CPWindow/CPWindow.j: Add isExcludedFromWindowsMenu and setExcludedFromWindowsMenu:, and keep the window's item current when the window is ordered in or out, retitled, made main or no longer main, miniaturized, deminiaturized or closed.
* Tests/AppKit/CPApplicationWindowsMenuTest.j: Add tests for listing, retitling, exclusion, the main window check mark, separator handling, file name titles and moving items to another Windows menu.
* Tests/Manual/TextEditor/WORKLIST.md: Remove the entry for this gap, and record the Window menu as tested.
