[WIP] Add CollectionContainsConstraint class to NUnit

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>There is no CollectionContainsConstraint</issue_title>
<issue_description>There is documentation for a CollectionContainsConstraint but no such class consists in the NUnit source code.

The documentation shows examples of code that internally call: new SomeItemsConstraint(new EqualConstraint(expected));
That is mentioned in the Notes section of the article.

The article contents is correct, except for the title and constructor part.
The examples are short cuts to other constraints.
</issue_description>

Comments on the Issue (you are @copilot in this section)

@mikkelbu I can see that I removed the constraint in 2017 - see nunit/nunit#1324 for context @OsirisTerje The documentation has examples that works, but they are using the SomeItemsConstraint.

The examples under CollectionContainsConstraint should be moved into SomeItemsConstraint

Then the CollectionContainsConstraint should be deleted, and also the toc.yml should be updated to remove this entry.

• Fixes There is no CollectionContainsConstraint #909

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