Exclude base resolver at the cop level

What does this MR do?

This removes the need to manually exclude BaseResolver from the ResolverType spec.

The base resolver does not need a type, since it is an abstract class.

See: #281697 (closed)

As a developer-facing change, no changelog is necessary.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.