Allow getTotalLength() and getPointAtLength() for <circle>, <rect> etc

Hi all

Given that we are now defining a "start point" for dashing for elements
other than path (circle, rect, etc).  Would it not now also make sense to
allow getTotalLength() and getPointAtLength() for these elements?

Among other things, it would be useful for people who want to use the
dasharray trick to animate the line drawing of shapes other than paths.

Moving these methods to the SVGGeometryElement interface might be
appropriate. However that is complicated by the fact that SVGGeometryElement
also covers text elements.  Perhaps, in the case of text, the "length"
might refer to the text baseline?

Paul