Making the htmx-indicator more accessible

[dorrzun]

Very brief, but shouldn't the approach HTMX takes for loading indicators use the visibility property from CSS?

The current approach is a bit of an old hack that would make sense on pre 2015 browsers, but surely we could move the goalpost at this point?
https://htmx.org/docs/#indicators

[dorrzun]

This behavior is already present, but the documentation fails to mention it.