[whatwg] Document.title for SVG documents

[Cameron McCormack]

Currently, HTML defines Document.title on SVG documents to defer to 
whatever the SVG specification defines for SVGDocument.title.  The 
SVGDocument interface has gone away, so this will need to be updated. 
From some basic testing, it looks like SVG needs the same behaviour as 
HTML -- first <title> element in the document, plus the white space 
collapsing behaviour.

Do you want to just handle that all in HTML?  I'm not sure there's much 
value to duplicating either the searching for the title element or the 
white space collapsing behaviour in SVG itself.