new primitive: transition, similar to modifiers, except they block certain render events

I don't know if this is feasible yet, but i was just looking at svelte, and https://twitter.com/ankurpsinghal/status/1640842168288919552?s=20
It seems that they may have transition managers, much like how we have modifier managers, so different animation implementations could be built on top of that.

Why not use modifiers? Modifiers don't and can't block the removal of an element from the DOM.

Thoughts?

Examples:
- https://github.com/ankurrsinghal/svelte-legos/blob/master/src/lib/transitions/roll/index.ts
- https://github.com/ankurrsinghal/svelte-legos/blob/master/src/lib/transitions/slide/index.ts
- https://svelte.dev/tutorial/animate
- https://blog.logrocket.com/essential-transitions-and-animations-in-svelte/

Alternatively, if the modifier manager had an option for blocking removal, we could probably reuse more code.
We would also need #883 for pre-paint timing, so animations could have a proper initial state