Rework class loading for reports with regards to `org.apache.maven.doxia.sink.impl.SinkEventAttributeSet`

[kwin]

Affected version

2.0.0

Bug description

The class loading behaviour of reports leads to potentially different versions of doxia-sink-api and doxia-core. Although the latter was initially thought for being used inside Doxia only it was used also in lots of reports (e.g. https://github.com/apache/maven-changes-plugin/blob/6cea480813789a2b366cbc6a7909a50390c493f6/src/main/java/org/apache/maven/plugins/changes/issues/AbstractIssuesReportRenderer.java#L25 or https://github.com/apache/maven-project-info-reports-plugin/blob/ec887bf3f20d0036b9bda5ef5a389b5659cf0952/src/main/java/org/apache/maven/report/projectinfo/DependencyConvergenceReport.java#L306).

If the impl in doxia-core is much older than its API in doxia-sink-api one runs into issue like observed in the context of apache/maven-site-plugin#1245.