Convert tests/src/Functional/PathologicTest.php to a Kernel test

Setting this to be related to version 2.0.x-dev, where subsequent development is happening; I'm not sure how valuable this would be to have in the 8.x-1.x branch, given D8's EOL, but if important, we could backport it.

1. As of 📌 Strip HTML tags when using assertEquals() to compare markup Fixed , assertEquals() strips all HTML markup, so we need to use assertSame() instead.
2. I replaced file_create_url() with the \Drupal::service('file_url_generator')->generateAbsoluteString. This appears still to return http://localhost/vfs://root/sites/simpletest/78243062/files/image.jpeg, however, but I'd like to see this fail on d.o output. The "no_vfs" patch exludes this for comparison purposes but is otherwise the same.
3. I moved one existing procedural helper function into the test class; this might subsequently better go in a test trait?
4. I added a new helper function, runFilter(), simply for DX benefit so that the individual assertions are easier to read.
5. There's also a fair amount of code syntax standards cleanup.

Fabulous, thanks!

1. Committed #2 as its own commit.
2. Committed #4 as you for separate history.
3. Added another commit to remove the bogus usage of t() for the test assertion messages.
4. Tested on 2.0.x.
5. Cherry-picked the 3 commits to 8.x-1.x and tested.
6. Pushed all commits to both branches.

Calling this fixed. Thanks again!
-Derek

Automatically closed - issue fixed for 2 weeks with no activity.