refactor(@angular/build): support `image-file` loader import attribute type

[clydin]

An additional loader import attribute value specialized for image files (loader: "image-file") is now available. This loader type is intended for use with the AOT compiler's optimized image instruction. It provides the same behavior as the file type with the addition of two named exports for the width and height of the image. The image-size package is used internally to determine image dimensions and all image types support by that package are also supported here. This loader type is currently not considered part of the public API and is only intended for use by the AOT compiler at this time.