Add JUnit-specific metadata to open-test-reporting's HTML report

[marcphilipp]

Overview

When creating the event-based XML report, the OpenTestReportGeneratingListener includes JUnit-specific metadata: type, unique ID, and legacy reporting name. This PR implements open-test-reporting's Contributor SPI to include that data in the new HTML report of open-test-reporting.

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Definition of Done

• There are no TODOs left in the code
• Method preconditions are checked and documented in the method's Javadoc
• Coding conventions (e.g. for logging) have been followed
• Change is covered by automated tests including corner cases, errors, and exception handling
• Public API has Javadoc and @API annotations
• Change is documented in the User Guide and Release Notes