fix(a): handle SVGAElement differently from HTML anchor tag

Before this change, SVG elements without an 'href' attribute (but with an
xlink:href attribute) within the application would always have their click
event preventDefault, due to the href attribute being falsy.

This change fixes this by giving an SVGAElement a separate link function which
is concerned with the xlink:href attribute.

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Some proper E2E testing would test this feature much more effectively.

Closes #5896