MenuSection insertion doesn't work, but docs suggest it should

[peterflynn]

Add this code to any extension:

Menus.getMenu(Menus.AppMenuBar.FILE_MENU)
    .addMenuItem(Commands.TOGGLE_USE_TAB_CHARS, null, Menus.LAST, Menus.MenuSection.FILE_SAVE_MENU);

Result: Menu item is added to the bottom of the File menu.
Expected: Added below Save, above Live File Preview.

The docs on MenuSection and on addMenuItem() both imply that using MenuSection constants works, but afaik from looking at the code we never got around to implementing it. If we don't have time to add the functionality now, we should remove the constants for now & update docs to say it isn't supported.

[peterflynn]

Nominating for Sprint 11 since it'd be good to have the menu APIs stabilized by then.

[redmunds]

FBNC back to @peterflynn

[peterflynn]

Darn GitHub autoclosing... reopening until I can actually verify...

[peterflynn]

Hmm... bug is mysteriously closed again. One more try at reopening here...

[peterflynn]

Confirmed fixed, but filed new bugs #1292 and #1293