feat: configure whether or not to lazy load

I'm using an `ion-icon` in a dropdown interface, where a user has to click an element to show the dropdown's content. Because of how ionicons is implemented, the icons inside the dropdown are not loaded instantly because the request is performed when it is visible to the user.

This, of course, is not ideal, as it shows a flicker while the icons are not downloaded. Just like what happens when you set a `background-image` to an element in its `:hover` state.

Is there any way to force the load of invisible icons?