Convert Rest ResourceTestBase to a kernel test

Problem/Motivation

Since this is for tests of JSON resources, there is no checking of any HTML. Therefore, this test base (and thus the tests that subclass this) could be a kernel test instead.

This would convert 5 browser tests to kernel tests.

Steps to reproduce

Proposed resolution

Merge request link

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet