Create AssetSaver implementations for each format.

[andriyDev]

Bevy now has AssetSaver. This allows a cross-platform way of saving assets by:

1. Getting an AssetWriter from an AssetSource (from AssetServer)
2. Calling AssetWriter::write to get an AsyncWrite object.
3. Calling AssetSaver::save with that AsyncWrite object.

In the future this will likely be streamlined but for now we should support AssetSaver to support this "canonical" workflow.

[NiklasEi]

For reference: the postcard feature already includes an asset saver

bevy_common_assets/src/postcard.rs

Lines 102 to 118 in 7618bc5

	impl<A: Asset + for<'de> Deserialize<'de> + Serialize> AssetSaver for PostcardAssetSaver<A> {
	type Asset = A;
	type Settings = ();
	type OutputLoader = PostcardAssetLoader<A>;
	type Error = PostcardAssetError;
	async fn save<'a>(
	&'a self,
	writer: &'a mut bevy::asset::io::Writer,
	asset: bevy::asset::saver::SavedAsset<'a, Self::Asset>,
	_settings: &'a Self::Settings,
	) -> Result<<Self::OutputLoader as AssetLoader>::Settings, Self::Error> {
	let bytes = to_stdvec(&asset.get())?;
	writer.write_all(&bytes).await?;
	Ok(())
	}
	}