Add block editor tests

[tiagomar]

Description

After the classic editor was made unavailable for new posts a couple of tests covering post creation were disabled.
Since the ability to create a post is considered critical to be automated, this PR adds a few tests to the new block editor covering the disabled scenarios and a new scenario covering the HTML mode.

• publishSimplePost: checks that a simple post with only title and text can be published.
• publishFullPost: checks that a post with title, text, image, category and tag can be published.
• blockEditorCanDisplayElementAddedInHtmlMode: checks that an element aded in HTML Mode can be displayed in Visual mode.

Testing Instructions

• The Connected Tests-2 CI job is green, and you can see publishSimplePost,publishFullPost and blockEditorCanDisplayElementAddedInHtmlMode tests included.
• Associated Firebase execution is also green (Firebase console access is needed to check this).
• Tests run locally on Pixel 2 API 28 (this is the model used on CI).

Regression Notes

1. Potential unintended areas of impact
   Changes would only affect ui tests.

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   Checked that all tests are passing locally an on CI.

3. What automated tests I added (or what prevented me from doing so)

• publishSimplePost
• publishFullPost
• blockEditorCanDisplayElementAddedInHtmlMode

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APKs:

• Jetpack-pr-15741-build-117945.apk

• WordPress-pr-15741-build-117945.apk

[tiagomar]

🤔 Having the assertion failure message as the first argument makes the code a bit confusing. assertTrue(boolean condition, String message) would make it better to read. ¯\_(ツ)_/¯

[jostnes]

Completely agree with that, I needed a second look to see that that was supposed to be the error message.

[jostnes]

Added a curious question and a comment on the verification point for one of the test cases.

I don't understand the framework enough to give constructive comments, but the tests looks good to me!

[jostnes]

Completely agree with that, I needed a second look to see that that was supposed to be the error message.

[jostnes]

The tests look good to me! Tested this locally and tests are working as expected. CI runs are green as well.