Recreate/copy Claro tests to Gin 6.x

It turns out that 11.2.x only has two tests:
* core/themes/claro/tests/src/Functional/NodeTitleTest.php
* core/themes/claro/tests/src/Functional/MenuLinkDefaultFormTest.php

I'll review them to see whether each test is also covered by a Gin test.

Doing a quick copy & adjust.

I copied the two tests and adjusted their namespaces.

When I ran NodeTitleTest locally the test failed because the output doesn't have a H1 tag, so I think we should remove that one.