native popovers

1. Some examples for the new [Popover API](https://developer.mozilla.org/en-US/docs/Web/API/Popover_API) would be helpful.
2. There might be some opportunities to provide targeted support in HTMX to make it easier to create rich popovers (e.g. [nested popovers](https://developer.mozilla.org/en-US/docs/Web/API/Popover_API/Using#nested_popovers)) so that developers don't need to write little bits of JS themselves to make things like menus.