Add comprehensive Views integration tests

Looking at how node module does its views testing:

- there is a single test module, which pretty much only exists to provide test views.
- however, these views aren't in config/install/, but in test_views/. This is a special folder that a views test class helper recognizes. Each test defines a class variable public static $testViews. These are both picked up by ViewTestData::createTestViews().

It seems a bit fiddly, but presumably this is to avoid either installing all the views in each test, or having a multitude of test modules.

So we should copy this pattern, and then come up with something similar to install the flags each test needs.

Before we code anything though, I think we should plan out what needs testing, and then from that, make a list of what config we need for each test.

7 years without any activity. I think we can close it as outdated. Please reopen if needed.