Fix R/B channel swap in Android raw pixel data

[mrousavy]

What

On Android, an ARGB_8888 Bitmap's memory is physically [R, G, B, A] bytes. The ARGB in the config name only describes the getPixel()/setPixel() ColorInt packing (0xAARRGGBB), not the layout that copyPixelsFromBuffer/copyPixelsToBuffer (raw memory copies) use.

Two coupled bugs made every raw pixel roundtrip swap red and blue on little-endian devices:

• loadFromRawPixelData (slow path) packed ColorInt-ordered words and wrote them with copyPixelsFromBuffer, so on little-endian they landed as B, G, R, A bytes.
• toRawPixelData labeled ARGB_8888 exports as BGRA, but the raw-copied bytes are physically R, G, B, A.

Fix

• Pack the physical pixel word (0xAABBGGRR) in the slow path.
• Label ARGB_8888 exports as RGBA.
• Re-key the byte-identical raw-copy fast path from BGRA to RGBA, so BGRA input now goes through the corrected swizzle path.
• Export PixelFormat, RawPixelData, EncodedImageData and ImageFormat from the entrypoint.

Note for consumers

This is a behavior fix. Code that worked around the swap by mislabeling RGBA bytes as 'BGRA' on Android must drop that workaround (for example react-native-vision-camera's harness tests).

Regression tests covering this land separately so they can validate all of the raw pixel data fixes together.

🤖 Generated with Claude Code

[patrickkabwe]

@mrousavy ran into this issue on android toRawPixelData() reports BGRA for ARGB_8888 bitmaps, but the bytes are actually RGBA so red and blue come out swapped if you read the buffer using the format it hands you. Here's a snippet that shows it

const image = await Images.loadFromFileAsync(anyColourfulPhoto)
const raw = await image.toRawPixelDataAsync()
const bytes = new Uint8Array(raw.buffer)
// Mean of each byte position across the image.
const means = [0, 1, 2, 3].map((k) => {
  let sum = 0
  for (let i = k; i < bytes.length; i += 4) sum += bytes[i]
  return sum / (bytes.length / 4)
})
console.log(raw.pixelFormat, means)
// Android: 'BGRA' [122.9, 124.7, 102.8, 255]  <- byte 0 is red, not blue
// iOS:     'BGRA' [103.2, 125.5, 123.3, 255]  <- byte 0 is blue, as reported

I tested this PR in both debug and release build it fixes the issue.

[mrousavy]

thanks for your feedback! lgtm then