[leaflet] DivIconOptions.html is too restrictive #75042

The html argument to L.divIcon currently is marked as string | HTMLElement | false | undefined:

This parameter is passed directly to HTMLDivElement.appendChild when options.html instanceof Element, so DivIcon can accept any elements, not just HTML ones: https://github.com/Leaflet/Leaflet/blob/d15112c9e8ac339f0f74f563959d0423d291308d/src/layer/marker/DivIcon.js#L49.

A good example of a non-HTML element which can realistically put as the icon would be an SVGSVGElement.