Add geometric primitives to bevy_math::prelude (#11432)

# Objective

Currently, the `primitives` module is inside of the prelude for
`bevy_math`, but the actual primitives are not. This requires either
importing the shapes everywhere that uses them, or adding the
`primitives::` prefix:

```rust
let rectangle = meshes.add(primitives::Rectangle::new(5.0, 2.5));
```

(Note: meshing isn't actually implemented yet, but it's in #11431)

The primitives are meant to be used for a variety of tasks across
several crates, like for meshing, bounding volumes, gizmos, colliders,
and so on, so I think having them in the prelude is justified. It would
make several common tasks a lot more ergonomic.

```rust
let rectangle = meshes.add(Rectangle::new(5.0, 2.5));
```

## Solution

Add `primitives::*` to `bevy_math::prelude`.

---------

Co-authored-by: Alice Cecile <[email protected]>

Author: Jondolf

crates/bevy_math/src/lib.rs

@@ -27,8 +27,9 @@ pub mod prelude {
             CubicBSpline, CubicBezier, CubicCardinalSpline, CubicGenerator, CubicHermite,
             CubicSegment,
         },
-        primitives, BVec2, BVec3, BVec4, EulerRot, FloatExt, IRect, IVec2, IVec3, IVec4, Mat2,
-        Mat3, Mat4, Quat, Ray2d, Ray3d, Rect, URect, UVec2, UVec3, UVec4, Vec2, Vec2Swizzles, Vec3,
+        primitives::*,
+        BVec2, BVec3, BVec4, EulerRot, FloatExt, IRect, IVec2, IVec3, IVec4, Mat2, Mat3, Mat4,
+        Quat, Ray2d, Ray3d, Rect, URect, UVec2, UVec3, UVec4, Vec2, Vec2Swizzles, Vec3,
         Vec3Swizzles, Vec4, Vec4Swizzles,
     };
 }

examples/3d/3d_viewport_to_world.rs

@@ -29,8 +29,7 @@ fn draw_cursor(
     };
 
     // Calculate if and where the ray is hitting the ground plane.
-    let Some(distance) =
-        ray.intersect_plane(ground.translation(), primitives::Plane3d::new(ground.up()))
+    let Some(distance) = ray.intersect_plane(ground.translation(), Plane3d::new(ground.up()))
     else {
         return;
     };