Add test for mesh transformations

[greeble-dev]

Objective

Add a test that will repro issues with mesh transformations, like #17992.

Solution

The PR adds a test_transform_mesh example that transforms a mesh in three different ways - each transformation should have the same visual result.

The screenshot shows the test reproducing #17992 - mesh 1 should have matched mesh 2 and 3.

The mesh uses an anisotropic material so that mesh tangents and normals are significant.

Concerns

• Right now the test is not suitable for screenshot comparison - the light is animated.
• Anisotropy is arguably an imprecise way to verify tangents and normals. But it's convenient and does everything in a single screenshot.

Testing

Tested on Win10/Vulkan/Nvidia.

cargo run --example test_transform_mesh --features "pbr_anisotropy_texture"

[greeble-dev]

CI failure appears unrelated to the PR.

https://github.com/bevyengine/bevy/actions/runs/13727867039/job/38398331235?pr=18194#logs

Run cargo deny check advisories
error[unmaintained]: paste - no longer maintained
    ┌─ /home/runner/work/bevy/bevy/Cargo.lock:369:1
    │
369 │ paste 1.0.15 registry+https://github.com/rust-lang/crates.io-index
    │ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ unmaintained advisory detected
    │
    ├ ID: RUSTSEC-2024-0436
    ├ Advisory: https://rustsec.org/advisories/RUSTSEC-2024-0436

[mockersf]

rather than using anisotropy, didn't we use to have a debug view to show tangents/normals?

[greeble-dev]

The shader_prepass example shows normals, but I couldn't find anything that shows tangents. Although a TangentPrepass might be a valid (if somewhat niche) feature?

(EDIT: Noticed this abandoned PR that added debug materials: #7390)

I also considered drawing a per-vertex gizmo. But that doesn't cover the third test case which validates transforms in the shader.

So my guess is that anisotropy is the least worst choice right now for showing that both tangents and normals are correct.

[greeble-dev]

Requiring feature pbr_anisotropy_texture is a bug in the shader. The example doesn't actually use anisotropy textures. I'll file an issue if this PR goes through.