SECURITY: Do not allow users to undelete a page they can't edit or create

SECURITY: Do not allow users to undelete a page they can't edit or create

If the page exists, it only checks edit rights, otherwise it
checks both edit and create rights.

This would only matter on wikis that have a non-default rights
configuration where there are users with undelete rights but a
restriction level enabled that prevents them from creating/editing
pages (or they otherwise aren't allowed to edit/create)

It should be noted that the error messages aren't used in the
normal UI currently, but they could be in the future, and
extensions could potentially be using them (The backend functions
return them, but the UI functions in Special:Undelete ignore
them)

Bug: T108138
Change-Id: I164b80534cf89e0afca264e9de07431484af8508