First-party parallax backgrounds

[alice-i-cecile]

What problem does this solve or what need does it fill?

Parallax backgrounds are a vital part of traditional 2D sidescrolling games like platforms.

The technology required to do this well is well-understood: Bevy should ship with a solution for this to make making 2D games in Bevy nicer.

This problem space is well-explored: we should implement and ship this, much like we do for various PBR features in 3D.

What solution would you like?

Upstream a working parallax solution like https://crates.io/crates/bevy-parallax

This could either go in bevy_sprite (behind a feature-flag) or in its own crate. No strong feelings there.

What alternative(s) have you considered?

We could also re-implement this from scratch, but I'd want to see clear problems with ecosystem crates first.

Additional context

Any other information you would like to add such as related previous work,
screenshots, benchmarks, etc.