Fix hydration error suspense (#4640)

* Fix hydration of error boundaries

* add a regression test

* add more comments

* fix typos

* more typos

* fix clippy

packages/playwright-tests/fullstack-errors.spec.js

@@ -0,0 +1,13 @@
+// @ts-check
+const { test, expect } = require("@playwright/test");
+
+test("errors", async ({ page }) => {
+  await page.goto("http://localhost:3232");
+
+  // Make sure the error that was thrown on the server is shown in the error boundary on the client
+  const errors = page.locator("#error-fallback-button");
+  await expect(errors).toContainText("Error fallback button clicked 0 times");
+  // Make sure the fallback is interactive
+  await errors.click();
+  await expect(errors).toContainText("Error fallback button clicked 1 times");
+});