Ensure Bevy's rendering byte usage is little-endian (#15750)

# Objective

- Fixes (partially) #15701.

## Solution

- Use little-endian bytes over native-endian bytes where applicable.

## Testing

- Ran CI.

## Open Questions

- Should we config-gate these for big-endian targets? It looks like
there are [very few
targets](https://doc.rust-lang.org/nightly/rustc/platform-support.html)
that use big-endian.

crates/bevy_image/src/hdr_texture_loader.rs

@@ -54,10 +54,10 @@ impl AssetLoader for HdrTextureLoader {
  for rgb in image_buffer.pixels() {
  let alpha = 1.0f32;
 
- rgba_data.extend_from_slice(&rgb.0[0].to_ne_bytes());
- rgba_data.extend_from_slice(&rgb.0[1].to_ne_bytes());
- rgba_data.extend_from_slice(&rgb.0[2].to_ne_bytes());
- rgba_data.extend_from_slice(&alpha.to_ne_bytes());
+ rgba_data.extend_from_slice(&rgb.0[0].to_le_bytes());
+ rgba_data.extend_from_slice(&rgb.0[1].to_le_bytes());
+ rgba_data.extend_from_slice(&rgb.0[2].to_le_bytes());
+ rgba_data.extend_from_slice(&alpha.to_le_bytes());
  }
 
  Ok(Image::new(

crates/bevy_image/src/image_texture_conversion.rs

@@ -119,10 +119,10 @@ impl Image {
  let b = pixel[2];
  let a = 1f32;
 
- local_data.extend_from_slice(&r.to_ne_bytes());
- local_data.extend_from_slice(&g.to_ne_bytes());
- local_data.extend_from_slice(&b.to_ne_bytes());
- local_data.extend_from_slice(&a.to_ne_bytes());
+ local_data.extend_from_slice(&r.to_le_bytes());
+ local_data.extend_from_slice(&g.to_le_bytes());
+ local_data.extend_from_slice(&b.to_le_bytes());
+ local_data.extend_from_slice(&a.to_le_bytes());
  }
 
  data = local_data;

crates/bevy_render/src/diagnostic/internal.rs

@@ -474,14 +474,14 @@ impl FrameData {
 
  let timestamps = data[..(self.num_timestamps * 8) as usize]
  .chunks(8)
- .map(|v| u64::from_ne_bytes(v.try_into().unwrap()))
+ .map(|v| u64::from_le_bytes(v.try_into().unwrap()))
  .collect::<Vec<u64>>();
 
  let start = self.pipeline_statistics_buffer_offset as usize;
  let len = (self.num_pipeline_statistics as usize) * 40;
  let pipeline_statistics = data[start..start + len]
  .chunks(8)
- .map(|v| u64::from_ne_bytes(v.try_into().unwrap()))
+ .map(|v| u64::from_le_bytes(v.try_into().unwrap()))
  .collect::<Vec<u64>>();
 
  let mut diagnostics = Vec::new();