Add e2e test for `ContentTemplates` feature

Ok, I think I rebased this correctly @bnjmnm

@bnjmnm: This MR looks fantastic — I had no idea this was passing all the way back in October! 🤯😱

If so, I'd have merged this as soon as it was green!

@jptaranto: thanks so much for getting this to a mergeable state again! 💙

Looks like we're down to a fairly simple remaining bit?

$ npm run test:playwright
> @drupal-canvas/root@0.0.0 test:playwright
> playwright install && playwright test
Error: Cannot find module './utilities/DrupalFilesystem'
Require stack:
- /builds/project/canvas/_drupal/web/modules/contrib/canvas/tests/src/Playwright/templates-linking.spec.ts
- /builds/project/canvas/_drupal/web/modules/contrib/canvas/node_modules/playwright/lib/transform/transform.js
- /builds/project/canvas/_drupal/web/modules/contrib/canvas/node_modules/playwright/lib/common/configLoader.js
- /builds/project/canvas/_drupal/web/modules/contrib/canvas/node_modules/playwright/lib/program.js
- /builds/project/canvas/_drupal/web/modules/contrib/canvas/node_modules/@playwright/test/cli.js
   at templates-linking.spec.ts:5
  3 | import { test } from './fixtures/DrupalSite';
  4 | import { Drupal } from './objects/Drupal';
> 5 | import { getModuleDir } from './utilities/DrupalFilesystem';
    | ^
  6 |
  7 | // Each object property is a prop type with a value of an array of the available
  8 | // suggestions to it.
    at Object.<anonymous> (/builds/project/canvas/_drupal/web/modules/contrib/canvas/tests/src/Playwright/templates-linking.spec.ts:5:1)

Postponing issue awaiting merge of #3571599: "Template for Basic page not found" error after adding new template which has poached one of the tests originally implemented in this MR and resolved some further issues.

This issue can be returned to once that one has landed.

#3571599: "Template for Basic page not found" error after adding new template landed!

I think there is a bug (well, more specifically a performance issue) that is resulting in this test failing.

When you link a prop on the `all props` SDC locally the PATCH request takes between 1.4 and 2 seconds on the server. Compare that to a Code component with just 1 prop which takes around 100ms.

On CI the test seems to keep failing and as far as I can deduce from the videos I'm seeing of the test playing back the issue is that linking the prop is taking over 8 seconds and that's causing some kind of time out. The test/functionality is working, it's just performing so slowly that the test runner is giving up waiting for it.

I think there is a bug (well, more specifically a performance issue) that is resulting in this test failing.

When you link a prop on the `all props` SDC locally the PATCH request takes between 1.4 and 2 seconds on the server. Compare that to a Code component with just 1 prop which takes around 100ms.

I spotted an inefficiency where we were calling for suggestions within a loop multiple times when once before the loop would suffice. I think this is a fairly simple fix but we'll see...

#17++ 👏

Reviewed the MR — some good progress here, some Qs.

🤦 although I got this back to passing everything, I realized there are linking options that have been added since this was originally created a few months back. The tests need to reflect those additions AND be able to recognize when such additions occur.

Tests have been updated to fail if new options are available for a given prop type or a linker is present that is not included in the tests, and it's current with 1.x overall.

Merged! It's critical that these tests are in place ahead of #3562896: Manage props/page data forms with react-hook-form as without them there are large parts of the UI that are not covered that may be impacted by those changes.