Convert views_test_data.module to OOP and remove it

Postponed on 📌 Convert function_exists() to is_callable() Active

Views access callbacks cannot be OOP until that is changed. I will push up converting what I've done so far and change that function_exists to is_callable, but it exits in a child process.

I'm not sure where the template preprocess initial preprocess goes either.
template_preprocess_views_view_mapping_test is the template function, but there is no hook_theme for views_view_mapping_test. Is this meant to be just a

I see:

#[ViewsStyle(
  id: "mapping_test",
  title: new TranslatableMarkup("Field mapping"),
  help: new TranslatableMarkup("Maps specific fields to specific purposes."),
  theme: "views_view_mapping_test",
  display_types: ["normal", "test"],
)]

But I am not sure where to put this. Is this another that is meant to be just a normal preprocess?

This is testing the generic theme definitions in views module.

I think it makes sense to convert that there to verify it works for other modules

I'm ok with converting the preprocess there. It is the callbacks are postponed.

I just figured i would do both at once until I got the is callable issue.