[ENH]: Accessibility for SVG hyperlinks

[jonblatho]

Problem

Currently matplotlib supports adding hyperlinks in SVGs, but (I believe) it lacks support for setting an aria-label attribute on links to improve accessibility.

Proposed solution

Alongside existing functionality to provide URLs for SVG hyperlinks (like the url= arg and set_urls()), a user should be able to provide corresponding aria-label attributes to be set for <a> tags.

Additional context and prior art

An example use case for this is adding links to an SVG scatter plot for use on the web where the points are too densely packed to make text labeling feasible.

[story645]

I think this would be a follow on to #21328, which adds aria attributes to artist objects.