Make search redaction more robust

What does this MR do?

By applying redaction only to a few known classes, it turns out we're skipping it in a number of desirable cases. It's better to apply it unconditionally, providing a fallback for cases where a plain array has been returned to us.

In the tests, instead of stubbing out the policy framework, stub out the results given to us by our subclasses. This allows us to test the redaction logic itself.

Screenshots

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.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #201886 (closed)