Convert automated tests from Simpletest to PHPUnit

Here is the patch, please review.

WIP patch, does not include #2 as that isn't really what this issue is about, I'll merge that later or move to a different issue.

Progress.

Moving GlobalRedirectTest to a follow-up, that one is tough.

1. +++ b/tests/src/Functional/AssertRedirectTrait.php
   @@ -18,19 +18,30 @@ trait AssertRedirectTrait {
   +    $client = $this->getSession()->getDriver()->getClient()->getClient();
   

   could just use $this->getHttpClient()

2. +++ b/tests/src/FunctionalJavascript/RedirectJavascriptTest.php
   @@ -0,0 +1,280 @@
   +    // Wait on ajax is unpredictable, wait for one second.
   +    sleep(1);
   

   :( but probably safer to do both? In case it runs longer than 1 second?

3. +++ b/tests/src/FunctionalJavascript/RedirectJavascriptTest.php
   @@ -0,0 +1,280 @@
   +    // Filter  with non existing value.
   

   2 spaces! :D

And lots of uses of t() that can be removed, but that should probably not be done here

1. Didn't know that method, updated.
2. I'm not sure why, but adding the wait on ajax somehow resulted in an exception, that's why I went with 1s... there's some pretty funky ajax going on that form, I'm not sure if something goes wrong if I call wait for ajax and there's actually no ajax call pending: "RuntimeException : Unable to complete AJAX request.". But at the same time, I have to wait, because apparently when I submit when the ajax request is still active, then the value of that form field is dropped o.0.
3. fixed.

As discussed in slack:

The assertWaitOnAjaxRequest() weirdness might be the result from a 403 on the AJAX request in that scenario

Ok, that turned out to really be a bug, some paths can throw an access denied exception (not sure why a leading / would cause that, though).

Added a catch for that for now, that makes it work with a regular ajax wait.

Committed.

Nice, real JS testing that uncovers bugs :)