perf(data-table): only render table row content when expanded (#1211)

Closes #1209

src/DataTable/DataTable.svelte

@@ -497,6 +497,7 @@
               parentRowId = null;
             }}"
           >
+            {#if expandedRows[row.id] && !nonExpandableRowIds.includes(row.id)}
               <TableCell
                 colspan="{selectable ? headers.length + 2 : headers.length + 1}"
               >
@@ -504,6 +505,7 @@
                   <slot name="expanded-row" row="{row}" />
                 </div>
               </TableCell>
+            {/if}
           </tr>
         {/if}
       {/each}