Categorize errors separately from failures in xUnit results

What does this MR do?

We want to show errors separately from failures in xUnit test reports: #32046 (closed)

This MR handles the behind-the-scenes work to enable us to separate the failed test count/list from the error count/list in the test report MR widget.

The actual copy update will happen in the feature MR: !23476 (merged)

Technically, this MR:

• Marks error test cases with STATUS_ERROR in the jUnit parser (so far they have been marked STATUS_FAILED to get them to show up in the widget/count)
• Adds error_count, new_errors, existing_errors, and resolved_errors to mirror the existing failure_count and *_failures methods in the test suite/report comparers
• Adds cases to the existing specs to test the new error methods (jUnit parser spec, test report widget spec, etc.)
• Keeps the MR widget language exactly the same as it was, i.e. Found X failed/error test results out of X total tests

Screenshots

There should be no changes to the UI due to this MR

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry will be in feature MR
• [-] Documentation (if required) will be in feature MR
• 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

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