Restore mediawiki.toc dependency on mediawiki.util

Follows-up If0438b7b6f4649, which broken the toc toggle module
since it was no longer part of a global module (mediawiki.util)
but only added to individual pages by the parser.

While that is a superior load mechanism, it broke existing pages
due to parser cache. Not the general html cache for logged-out
users but the main parser cache, which affects logged-in users
as well.

Bug: 64765
Change-Id: Ia12998fb11c686e1cc965578f7beb31c79b1b12c