gestures: Avoid spreading non-iterable in older browsers

Instead just convert to array.

lib/utils/gestures.js

@@ -125,7 +125,7 @@ function canBeLabelled(el) {
  * @return {!Array<!HTMLLabelElement>} Relevant label for `el`
  */
 function matchingLabels(el) {
-  let labels = [...(/** @type {HTMLInputElement} */((el).labels || []))];
+  let labels = Array.prototype.slice.call(/** @type {HTMLInputElement} */(el).labels);
   // IE doesn't have `labels` and Safari doesn't populate `labels`
   // if element is in a shadowroot.
   // In this instance, finding the non-ancestor labels is enough,