Fix editor tests on Windows

- In #15373, we implemented copy/paste actions in using the system
clipboard.
For any reasons, on Windows, the clipboard doesn't contain the expected
data when the tests are ran in parallel, hence the tests which are
using the clipboard need to be ran sequentially.
- Make sure that we can paste after having copied.

test/integration/test_utils.js

@@ -87,3 +87,16 @@ function getSelectedEditors(page) {
   });
 }
 exports.getSelectedEditors = getSelectedEditors;
+
+async function waitForEvent(page, eventName, timeout = 30000) {
+  await Promise.race([
+    // add event listener and wait for event to fire before returning
+    page.evaluate(name => {
+      return new Promise(resolve => {
+        document.addEventListener(name, resolve, { once: true });
+      });
+    }, eventName),
+    page.waitForTimeout(timeout),
+  ]);
+}
+exports.waitForEvent = waitForEvent;