This moves search-one-offs.js into a jsm without making any substantive changes, adds a new subclass in UrlbarSearchOneOffs.jsm, and uses `UrlbarSearchOneOffs` in `UrlbarView` instead of the base `SearchOneOffs` class. `UrlbarSearchOneOffs` will be fleshed out in part 2. Differential Revision: https://phabricator.services.mozilla.com/D84784