Support icons in switch

[yringler]

We want to use the shoelace switch, but we need a way to add an icon inside it to show enabled/disabled.
For example - Atlassian design system

Would you accept a PR to add support for that to the sl-switch?
I was thinking two slots - one for checked, one for unchecked?

[claviska]

I'd be open to a clean PR to add these (probably through slots) but I think the default styling will be hard to get right with the thumb as big as it is.

In the meantime, here's a pen that might help.

CleanShot.2023-10-18.at.14.11.06.mp4