Watchlist – [1] Allow presentation of client side view controller over Component view

[staykids]

Phabricator: https://phabricator.wikimedia.org/T356794 (partially)

Notes

This is part of a series of PRs that adds the functionality to add new languages from the Watchlist Filter view. This PR adds the plumbing needed to present arbitrary views controlled by the client over the Watchlist feature Component view.

Test Steps

N/A – no user facing functionality (added in https://github.com/wikimedia/wikipedia-ios/pull/4747)