Newlines in data URI within HTML and SVG attributes should be allowed

See https://en.wikipedia.org/wiki/Data_URI_scheme#HTML.

According to this Wikipedia page, white space characters in XML attributes are ignored. This must be inaccurate, as ignoring any white space character in any attribute can't possibly be correct. It is also hard to believe that Saxon, which converts newlines in attributes to spaces, would be wrong on such a basic feature of XML. There must be another explanation for these things to be valid in HTML. Or perhaps it is not valid, but then Pipeline should still support it, as it is a common practice to break up long data URIs into lines.

@nicolegaines