v4 Proposal

[mixonic]

Following https://github.com/html-next/vertical-collection/issues/341, I propose a 4.0 branch and release.

Goals:

• Drop support for Ember < 3.12-LTS.
• v2 Ember addon? Is this even possible with the above constraint? I'm not sure. Maybe a nice to have. See https://github.com/html-next/vertical-collection/issues/260
• No change in Node support.
• Release 1.0 of https://github.com/html-next/ember-raf-scheduler.

[NullVoxPopuli]

is it possible to bump ember-cli-htmlbars to v6?, ref: https://github.com/html-next/vertical-collection/pull/371