[LiveComponent] auto-add `aria-busy="true"` during re-render

[kbond]

Something Ryan brought up in his livestream. I think this would help with accessibility but also allows styling loading state without using live-component specific stuff (https://tailwindcss.com/docs/hover-focus-and-other-states#aria-states).

[smnandre]

... and role="status" on the loaders

( https://getbootstrap.com/docs/5.0/components/spinners/#about )