R1:b2739710ba74

Don't allow forms which can't create objects to be added to profile menus

Summary:
Fixes T12281. Some forms (like Settings) can't actually create new objects. Currently, though, you can select them and add them to profile menus; if you do, they fail when building an item.

Kick them out of the typeahead, and decline to render them in menus.

Test Plan:
Added "Create Settings" to a menu, no longer fatals after patch (item vanished from menu, still editable normally to get rid of it).

Tried to add another…