Mesh2d `world_normal` and `world_tangent` computation is incorrect

## Bevy version and features

main

## What you did

Run `cargo r --example mesh2d` with tangents
```rust
Rectangle::default()
.mesh()
.build()
.with_generated_tangents()
.unwrap(),
```

## What went wrong

The `world_normal` and `world_tangent` in vertex output are incorrect, I expect they are the same as mesh normal and tangent:

Reproduce the issue with `cargo r --example mesh2d` using `Rectangle::default().mesh().build().with_generated_tangents()`. Start by tracing how the mesh2d example produces vertex `world_normal` and `world_tangent` values. Done means those outputs match the mesh normal and tangent shown in the report.

Written by the indexing model from the issue text.