Add on:focus handler to button to fix A11y issue

packages/bbui/src/Button/Button.svelte

@@ -30,6 +30,7 @@
     {disabled}
     on:click|preventDefault
     on:mouseover={() => (showTooltip = true)}
+    on:focus={() => (showTooltip = true)}
     on:mouseleave={() => (showTooltip = false)}
   >
     {#if icon}