Use collect to build mesh attributes (bevyengine#5255)

Small optimization. `.collect()` from arrays generates very nice code without reallocations: https://rust.godbolt.org/z/6E6c595bq

Co-authored-by: Kornel <kornel@geekhood.net>

crates/bevy_render/src/mesh/shape/mod.rs

@@ -92,15 +92,9 @@ impl From<Box> for Mesh {
  ([sp.max_x, sp.min_y, sp.min_z], [0., -1.0, 0.], [0., 1.0]),
  ];
 
- let mut positions = Vec::with_capacity(24);
- let mut normals = Vec::with_capacity(24);
- let mut uvs = Vec::with_capacity(24);
-
- for (position, normal, uv) in vertices.iter() {
- positions.push(*position);
- normals.push(*normal);
- uvs.push(*uv);
- }
+ let positions: Vec<_> = vertices.iter().map(|(p, _, _)| *p).collect();
+ let normals: Vec<_> = vertices.iter().map(|(_, n, _)| *n).collect();
+ let uvs: Vec<_> = vertices.iter().map(|(_, _, uv)| *uv).collect();
 
  let indices = Indices::U32(vec![
  0, 1, 2, 2, 3, 0, // top
@@ -160,14 +154,9 @@ impl From<Quad> for Mesh {
 
  let indices = Indices::U32(vec![0, 2, 1, 0, 3, 2]);
 
- let mut positions = Vec::<[f32; 3]>::new();
- let mut normals = Vec::<[f32; 3]>::new();
- let mut uvs = Vec::<[f32; 2]>::new();
- for (position, normal, uv) in &vertices {
- positions.push(*position);
- normals.push(*normal);
- uvs.push(*uv);
- }
+ let positions: Vec<_> = vertices.iter().map(|(p, _, _)| *p).collect();
+ let normals: Vec<_> = vertices.iter().map(|(_, n, _)| *n).collect();
+ let uvs: Vec<_> = vertices.iter().map(|(_, _, uv)| *uv).collect();
 
  let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
  mesh.set_indices(Some(indices));
@@ -204,14 +193,9 @@ impl From<Plane> for Mesh {
 
  let indices = Indices::U32(vec![0, 2, 1, 0, 3, 2]);
 
- let mut positions = Vec::new();
- let mut normals = Vec::new();
- let mut uvs = Vec::new();
- for (position, normal, uv) in &vertices {
- positions.push(*position);
- normals.push(*normal);
- uvs.push(*uv);
- }
+ let positions: Vec<_> = vertices.iter().map(|(p, _, _)| *p).collect();
+ let normals: Vec<_> = vertices.iter().map(|(_, n, _)| *n).collect();
+ let uvs: Vec<_> = vertices.iter().map(|(_, _, uv)| *uv).collect();
 
  let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
  mesh.set_indices(Some(indices));