The multi-category filter needs to be an actual set of labeled checkboxes

Looking into this at NEDCamp. Adding the issue tag.

The markup changes have been completed and the testing is all passing. This is ready for review.

fail - can't find by that selector. close, though!

    There was 1 failure:
    
    1)
    Drupal\Tests\project_browser\FunctionalJavascript\ProjectBrowserUiTestJsonApi::testMultiplePlugins
    Behat\Mink\Exception\ElementNotFoundException: Element matching css
    ".pb-filter__checkbox-label-txt" not found.    

I was able to get the tests all passing. Marking this as needs review.

install-state.gz should not be part of MR.

Working on the rebase now.

I rebased the code and confirmed all tests are now passing. Marking as needs review.

This MR needs re-roll.

Rebased and resolved conflicts. Test changes in tests/src/FunctionalJavascript/ProjectBrowserUiTestJsonApi.php are still pending and need to be moved to ProjectBrowserUiTest::testMultiplePlugins.

I have moved the changes from ProjectBrowserUiTestJsonApi::testMultiplePlugins to ProjectBrowserUiTest::testMultiplePlugins. I verified the output from the old testMultiplePlugins function and added the same flow to the ProjectBrowserUiTest::testMultiplePlugins.

Marking this as "Needs Review." Please review and let me know if this approach makes sense.

This is partly my fault. I fixed up the tests to work for the drop-downs. Rather than just plow in and work out selectors for the new markup, I should have asked can we make the checkboxes easier for the tests to select. I'll know better next time.

I have reviewed the changes and everything looks good to me. The revised selecters look much cleaner. I've also carried out a manual test, and everything seems to work correctly.

I note that the eslint check is failing due to the recipe.yml file. This file has not been touched by this change, so I think it's an unrelated issue, so I think it should be fixed in a separate issue.

This is much more semantic, and also will help with tests!