Feature: button ion-button icon-only is now a slot attribute of child element ion-icon

[dagobit]

If you used the directive "icon-only" within the button element:

<button ion-button icon-only>
 <ion-icon name="star"></ion-icon>
</button>

it now should be:

<ion-button>
 <ion-icon name="star" slot="icon-only"></ion-icon>
</ion-button>

currently any rule is replacing it, the result of ... --fix is:

<ion-button icon-only>
 <ion-icon name="star"></ion-icon>
</ion-button>