Display classname JUnit attribute in report modal

What does this MR do?

When JUnit report has <testcase classname="the-classname"> it's not being displayed in the reports modal. With this MR I've added support for displaying classname to the report.

Partially related to https://gitlab.com/gitlab-org/gitlab-ce/issues/50964 - In particular it solves https://gitlab.com/gitlab-org/gitlab-ce/issues/50964#note_133968247

Before

After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Style guides