Convert web tests of views

Proposed followups:

\Drupal\views\Tests\FieldApiDataTest needs FieldTestBase so omitting from this patch
\Drupal\views\Tests\ViewAjaxTest needs to be moved to a javascript test
\Drupal\views\Tests\ViewElementTest needs to be changed to a kernel test
\Drupal\views\Tests\Plugin\StyleGridTest needs to be changed to a kernel test
All Update tests need UpdatePathTestBase to be converted first
\Drupal\views\Tests\Plugin\StyleOpmlTest weird stuff happens when not working with HTML (or something, didn't dig deep)
\Drupal\views\Tests\Plugin\DisplayFeedTest is also using non-HTML pages so taken that out of this conversion
Created #2865336: Add \Drupal\simpletest\WebTestBase::assertBlockAppears to \Drupal\FunctionalTests\AssertLegacyTrait,

Notes:

\Drupal\views\Tests\ViewTestData not sure if we want to move this, so leaving it alone for now.
Updated \Drupal\Tests\views\Functional\ViewTestBase::helperButtonHasLabel to work with BTB (was using field to find a button, that doesn't work)
\Drupal\Tests\views\Kernel\Handler\AreaEmptyTest was split from \Drupal\Tests\views\Functional\Handler\AreaTest because it needed to be a kernel test and that required some changes to the methods used for testing.
\Drupal\Tests\views\Kernel\Plugin\ExposedFormRenderTest split of from \Drupal\Tests\views\Functional\Plugin\ExposedFormTest because it needed to be a kernel test
\Drupal\Tests\views\Kernel\Plugin\DisplayPageTest::testReadMore split from \Drupal\Tests\views\Functional\Plugin\DisplayTest and turned into a kernel test and added to \Drupal\Tests\views\Kernel\Plugin\DisplayPageTest (that sounded like the right place to put it)