`<Avatar>` Svelte component img should have width and height defined

[abovedave]

The <img> tag has zero width and height causing a brief layout shift before the image loads.

Stacks/packages/stacks-svelte/src/components/Avatar/Avatar.svelte

Line 92 in dc19e48

<img class="s-avatar--image" {src} alt="" role="presentation" />

[giamir]

Feel free to open a PR @abovedave. It should be a simple one I think. Thanks

[abovedave]

Will do, just wanted to log before I forgot