Extend UITester support for ArrayViewEditor

The goal would be to extend support for downstream projects to write tests that require interacting with the GUI objects created by ArrayViewEditor.

The ArrayViewEditor depends on TabularEditor, so testing support for ArrayViewEditor depends on testing support for TabularEditor.

Once testing support for TabularEditor is added, testing support for ArrayViewEditor can simply reuse whatever interaction and location logic registered for TabularEditor. This will likely reuse the redirection pattern we had for nested UI in simple InstanceEditor and custom InstanceEditor.

Actions:
(1) Add (toolkit agnostic) tests for the editor in TraitsUI, focus on interactions that are going to be useful downstream as well.
(2) Expand the testing support via the default target registry used by UITester

Optional and opportunistic: See if a test can be added for the demo using this editor (if there is one), related to #1257. It might also provide motivation as to what features are likely useful downstream.