Switch p5.js editor to use 2.x latest as the default version #4149

Please see the parent issue for timeline and context. Please feel free to raise questions, concerns, or overlooked tasks; however, the work will be done by the maintainers, so it is not open to implementation volunteers.

When this task is done, on the p5.js-web-editor repository, the released version of the editor will use the latest 2.x as default, rather than 1.x. Prior versions remain available as opt-in options.

Related (but not blocking) is to surface more clearly that all users who want to keep using the 1.x default can use this link: http://editor.p5js.org/?version=1 Bookmarking this link or using it in educational materials makes it possible to use v1.x as default, and not have to always pick a version manually.

Related (but not blocking) is this update to the auto-complete hinter.

When this task is done, the library management screen (below) should have "Default" next to whatever 2.x version is most recent.