feat(data-table): add ToolbarMenu

Requires menuRef from OverflowMenu to be exported.

src/DataTable/ToolbarMenu.svelte

@@ -0,0 +1,22 @@
+<script>
+  import { getContext } from "svelte";
+  import Settings16 from "carbon-icons-svelte/lib/Settings16";
+  import { OverflowMenu } from "../OverflowMenu";
+
+  const ctx = getContext("Toolbar");
+
+  let menuRef = null;
+
+  $: ctx.setOverflow(menuRef != null);
+  $: if (menuRef) menuRef.style.top = "100%";
+</script>
+
+<OverflowMenu
+  bind:menuRef
+  icon="{Settings16}"
+  {...$$restProps}
+  class="bx--toolbar-action bx--overflow-menu {$$restProps.class}"
+  flipped
+>
+  <slot />
+</OverflowMenu>