fix($location): parse xlink:href for SVGAElements

Before this fix, the xlink:href property of an SVG <a> element could not be
parsed on click, as the property is an SVGAnimatedString rather than a
DOMString.

This patch parses the xlink:href's animVal into a DOMString in order to
prevent an `Object #<SVGAnimatedString> has no method 'indexOf'` exception
from being thrown, and also to update the location if necessary as expected.

Fixes #5198