[Content]: `Translation` class and lazy I18n

[AugustMiller]

Plugin developers should have information about when to use craft\helpers\Translation::prep() and translate() over Craft::t().

Places that would be good to mention this:

• Static translations
• Queue Jobs
• A new Announcements page (we currently only mention them in the CP tour, and ought to let plugin devs know how to take advantage of them)