`com.sun.javafx.iio.ImageStorage` currently ignores the MIME image subtype specified for images encoded in data URIs. This should be improved as follows:

1. If the specified image subtype is not supported, an exception will be thrown.
2. If the specified image subtype is supported, but the data contained in the URI is of a different (but also supported) image format, the image will be loaded and a warning will be logged. For example, if the MIME type is "image/jpeg", but the image data is PNG, the following warning will be generated:

    Image format 'PNG' does not match MIME type 'image/jpeg' in URI 'data:image/jpeg;base64,iVBORw0KGgoAAA...AAAElFTkSuQmCC'

Also, the javadoc of `javafx.scene.image.Image` incorrectly states:

    94 * If a URL uses the "data" scheme, the data must be base64-encoded
    95 * and the MIME type must either be empty or a subtype of the
    96 * {@code image} type.

However, omitting the MIME type of a data URI is specified to imply "text/plain" (RFC 2397, section 2). Since the `com.sun.javafx.util.DataURI` class is implemented according to this specification, trying to load an image without MIME type correctly fails with an `ImageStorageException`: "Unexpected MIME type: text".

The solution is to fix the documentation.