Adapt to latest Theia version

[marcdumais-work]

Following this recent Theia commit [1], one now has to use "TheiaAppLoader.load()", to load a Theia application in a theia playwright templace. Some code here needs to be updated.

Also, use the latest versions (as of now) for @theia/playwright and @playwright/test

[1]: "Basic playwright electron support (#12207)"
eclipse-theia/theia@487e92b

[marcdumais-work]

I will also open a PR towards the main Theia repo to update the following documentation about using the new way of "loading" the app:

• https://github.com/eclipse-theia/theia/blob/master/examples/playwright/docs/GETTING_STARTED.md
• https://github.com/eclipse-theia/theia/blob/master/examples/playwright/docs/EXTENSIBILITY.md

[planger]

Thanks a lot @marcdumais-work, looks good to me and works fine! 👍

[marcdumais-work]

Thanks for the quick review @planger !
Ok to merge?

[marcdumais-work]

BTW, we have started to make use of this template and the related test infrastructure from @theia/playwright: we integrated the template as a starting point for a UI test suite in our eclipse-cdt-cloud/theia-trace-extension repo:
eclipse-cdt-cloud/theia-trace-extension#1052

[marcdumais-work]

Update: I noticed there's a workflow in this repository, but CI was disabled because it had not run in a couple of months, I was able to re-enable it in the GitHub UI (Actions tab) and manually launch the tests for this PR. It failed:
https://github.com/eclipse-theia/theia-playwright-template/actions/runs/8281847489/job/22661382243

I think it's missing some OS-level dependencies, for Theia to build. I will have a look, and since I probably need to update the workflow, I may as well clean it up similar to eclipse-theia/theia#13491

update: no extra apt dependency needed, when I look at theia main repo workflows. They do install node-gyp globally - maybe that's what's needed.

[marcdumais-work]

It turns-out that the Theia build issue was apparently caused by a later version of Python being pulled. Now the workflow uses 3.11, like Theia workflows, and Theia builds.

[planger]

Oh, thank you very much for re-enabling the CI and tracking down the CI issue!