Node::transform field

[ickshonpe]

Objective

Add UI node transform support with minimal changes.

Solution

• Add a transform field to Node.
• In layout updates apply the layout position translation to the transform field and then set_if_neq it to the node entity's Transform component.

Then leave propagate_transforms to update the GlobalTransforms.

Testing

Reviewers can look at the overflow_debug example, which is the only current UI example that modifies the transform.

[aevyrie]

Isn't this a bit anti-composition? The Node struct is absolutely ginormous. What's the motivation for not using Transform?

[ickshonpe]

Isn't this a bit anti-composition? The Node struct is absolutely ginormous.

Yep, this isn't good at all, it's just the minimum I thought might possibly get merged as an intermediate step towards some of the problems with the UI transforms. #8240 is my preferred approach but it's going to take forever to update for main and it's been really difficult to reach concensus on changes like this.

What's the motivation for not using Transform?

ui_layout_system sets UI node's Transform's translation with the position offset of the node, which overwrites any value users set to the translation field themselves. You can write a system that adjusts the translations post layout but before transform propagation but that's kind of horrible and a lot of attempts I've seen fail with a panic.

We could make Transform work by backing up the values of Transform before ui_layout_system runs and then restoring the values after the transforms are propagated but that seems really ugly.