Consider a more practical showcase for `2d_on_ui` example

[rparrett]

Alice mentioned a desire for a potential followup here: https://bsky.app/profile/alice-i-cecile.bsky.social/post/3lqnthgrcee2t so here's an issue with my thoughts.

For reference, the example PR: #18513.

Problem

The example currently shows a sprite rotating in ways that would be hard to achieve using pure UI, so it's demonstrating something potentially useful, but it's not clear to me at least what the practical applications might be.

The linked discussion listed as motivation for the PR proposes the following question:

I want to draw a texture, a 3D mesh, a minimap… anything! on top of the bevy UI. How do I do this?

But the answer to most of that in recent/upcoming versions of Bevy is pretty likely to involve ImageNode, ViewportNode, or UiMaterial.

Solution?

Ideally, we should find a compelling reason to draw on top of UI and rework the example slightly to show that.

We may also want to cross-reference other related examples.

Also

I think we should consider moving the example to the ui subfolder. The example is showing 2d stuff on UI, but the concept isn't really 2d-specific.

[alice-i-cecile]

Really helpful; thank you <3 Agreed on moving it, and double agreed on something a bit more grounded.

[theotherphil]

The example shows a rotating 2d sprite - the use of text was replaced after Alice’s initial feedback.

There’s a link to a video of this on #18513 (comment).

[rparrett]

The example shows a rotating 2d sprite - the use of text was replaced after Alice’s initial feedback.

Oops, I should have known better than to trust a PR description on a PR with that much feedback. Updated the issue description.