Function append_alpha

pub fn append_alpha(
    dst: &mut [f32],
    dst_stride: u32,
    src: &[f32],
    src_stride: u32,
    a_plane: &[f32],
    a_stride: u32,
    width: u32,
    height: u32,
)

Adds alpha plane into an existing RGB/XYZ/LAB or other 3 plane image. Image will become RGBA, XYZa, LABa etc.