Test coverage for the search process

Since I'm just learning about writing tests, I thought I'd give this one a quick review! Couple things that came up:

1. +++ b/tests/src/Functional/SearchTest.php
   @@ -0,0 +1,63 @@
   +    $user = $this->createUser(['perform search only']);
   

   The permission to get to the admin/content/scanner page is 'administer nodes', so the test user should have this permission as well.

2. +++ b/tests/src/Functional/SearchTest.php
   @@ -0,0 +1,63 @@
   +    $session_assert->fieldExists('replace');
   

   The 'replace' field only shows up if you have the permission 'perform search and replace', so either we need that permission on the createUser line above, or the "replace" field needs to be checked with a different user setup.

Here's the updated patch (and interdiff) with just that one difference to the user setup.

Changing this to Needs Work because it isn't testing the functionality yet.

Improving the tests and fixing a few deprecation notices.

Oh, actually, i just saw that there are separated issues for each test. The patch i sent was testing the replacement, sorry, changing back to needs work. I'll send the path in #3214130: Test coverage for the replacement process

@hmendes, great work on the tests.

Thanks @joseph.olstad. Adding a patch testing the "Search" functionality.

The tests are giving some errors regarding the problem in #3252911: Undefined index: count, Undefined index: entities in Drupal\scanner\Form\ScannerForm::batchSearch() (line 264.
I also didn't fixed the phpcs problems as they are already being fixed on #3214130: Test coverage for the replacement process, although i actually rather fix them in a separate issue.