responsive_image_build_source_attributes(ImageInterface $image, array $variables, BreakpointInterface $breakpoint, array $multipliers)
Helper function for template_preprocess_responsive_image().
Builds an array of attributes for <source> tags to be used in a <picture> tag. In other words, this function provides the attributes for each <source> tag in a <picture> tag.
In a responsive image style, each breakpoint has an image style mapping for each of its multipliers. An i