Core: Add ability to have separate render thread accessed through `window.on_tick`, which is called each display refresh.

[foxnne]

This PR depends on this PR which will need to be merged before we can update the zon here.

• [X] By selecting this checkbox, I agree to license my contributions to this project under the license(s) described in the LICENSE file, and I have the right to do so or have received permission to do so by an employer or client I am producing work for whom has this right.