Revert "refactor: updated screenshot.js to use dynamic module imports"

This reverts commit 2e6fc1e.

src/toolbar/preview/screenshot.js

@@ -1,11 +1,25 @@
+let html2canvasPromise;
+
 const screenshot = async () => {
   document.getElementById('prismic-toolbar-v2').setAttribute('data-html2canvas-ignore', true);
+  if (!html2canvasPromise) html2canvasPromise = script('https://html2canvas.hertzen.com/dist/html2canvas.min.js');
+  await html2canvasPromise;
+
+  const canvas = await window.html2canvas(document.body, {
+    logging: false,
+    width: '100%',
+    height: window.innerHeight,
+  });
+  return new Promise(resolve => canvas.toBlob(resolve, 'image/jpeg', 0.6));
+};
 
-  const options = { logging: false, width: '100%', height: window.innerHeight };
-
-  return import('https://html2canvas.hertzen.com/dist/html2canvas.esm.js')
-  .then(html2canvas => html2canvas(document.body, options))
-  .then(canvas => new Promise(resolve => canvas.toBlob(resolve, 'image/jpeg', 0.6)));
+function script(src) {
+  return new Promise(resolve => {
+    const el = document.createElement('script');
+    el.src = src;
+    document.head.appendChild(el);
+    el.addEventListener('load', () => resolve(el));
+  });
 }
 
 export default screenshot;