Add extensive hydration error test suite for Pages router

Pages router will support both React 18 and 19 which has significant changes for hydration errors.
The existing acceptance tests only cover App router which runs exclusive on React 19.

Ideally this would be a single test suite that just forks on the assertion. However, there are a lot of differences between App router and Pages router and putting that into a single file takes more time.

The goal here is to not regress any further with Pages router when extending support to 18.
Once RC2 landed, I'll merge these test suites.

Author: eps1lon

test/development/acceptance-app/hydration-error.test.ts

@@ -7,7 +7,7 @@ import { getRedboxTotalErrorCount } from 'next-test-utils'
 
 // https://github.com/facebook/react/blob/main/packages/react-dom/src/__tests__/ReactDOMHydrationDiff-test.js used as a reference
 
-describe('Error overlay for hydration errors', () => {
+describe('Error overlay for hydration errors in App router', () => {
   const { next, isTurbopack } = nextTestSetup({
     files: new FileRef(path.join(__dirname, 'fixtures', 'default-template')),
     skipStart: true,