fix(data-table): pass header key to TableHeader (#1114)

The id is needed to update the sort icon direction accordingly.

Fixes #1113

src/DataTable/DataTable.svelte

@@ -306,6 +306,7 @@
             <th scope="col"></th>
           {:else}
             <TableHeader
+              id="{header.key}"
               disableSorting="{header.sort === false}"
               on:click="{() => {
                 dispatch('click', { header });