Support BGRA images in Vello Classic

[sagudev]

This is possible because of linebender/peniko#120.

[DJMcNab]

This implementation looks reasonable to me.

We will need to bring this up at renderer office hours, but I think we can merge it optimistically before then.

However, I would like to see at least one test which uses this before landing.
The changelog update will need to be folded in with #1231.

[DJMcNab]

To clarify the state, this is still lightly blocked on a test. This only needs to be similar to:

vello/examples/scenes/src/test_scenes.rs

Lines 1803 to 1823 in 2bba591

	params.resolution = Some(Vec2::new(1100., 1100.));
	params.base_color = Some(palette::css::WHITE);
	let mut blob: Vec<u8> = Vec::new();
	[
	palette::css::RED,
	palette::css::BLUE,
	palette::css::CYAN,
	palette::css::MAGENTA,
	]
	.iter()
	.for_each(|c| {
	blob.extend(c.to_rgba8().to_u8_array());
	});
	let data = Blob::new(Arc::new(blob));
	let image = ImageBrush::new(ImageData {
	data,
	format: ImageFormat::Rgba8,
	width: 2,
	height: 2,
	alpha_type: ImageAlphaType::Alpha,
	});

That is, it can manually construct the image, rather than loading from a file.

[sagudev]

To clarify the state, this is still lightly blocked on a test.

I know, I am currently on vacation so progress is slow. I will rerequest review when ready.

This only needs to be similar to:

This is great example, thanks.

[DJMcNab]

Yeah, there's no rush! I'm just noting it e.g. for office hours, so we can keep track of an accurate state

[DJMcNab]

Thank you - this looks good. There are just a few details we should fix before landing this.

The concern about ImageQuality is especially blocking (plus CI, but as noted, just doing a hack for that is fine).

[DJMcNab]

I think this PR just needs the change to mask the qualities correctly after 9b37898, then we're done!

Thank you

[DJMcNab]

LGTM. Thanks!