Add supporting themes required for Lotusdocs

themes/hugo-mod-jslibs-dist/popperjs/package/lib/dom-utils/getHTMLElementScroll.js.flow

@@ -0,0 +1,8 @@
+// @flow
+
+export default function getHTMLElementScroll(element: HTMLElement) {
+  return {
+    scrollLeft: element.scrollLeft,
+    scrollTop: element.scrollTop,
+  };
+}