Invalidate cached pages when settings are updated

I wasn't planning to work on this today, but it was impossible to write tests 🐛 Fix the YouTube tracking setting Active without figuring this out. Consequently, I'm not planning to write a test for this specifically since the tests for the other issue will fail if this change is ever undone.

Adding a cache tag to pages with the attached JS isn't enough. Though we don't have to explicitly invalidate the tag; the entity system takes care of that for us. The real problem is that the module's library definitions are built dynamically. If the settings change, then the library definitions also have to be rebuilt in addition to invalidating the cached pages.

Automatically closed - issue fixed for 2 weeks with no activity.