Upgrade to Doxia 2.1.0

[kwin]

Upgrade to Reporting Exec 2.0.1
Upgrade IT to maven-changes-plugin 3.0 due to
apache/maven-doxia#1054 and apache/maven-reporting-exec#141.

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[kwin]

This fails in certain ITs due to Doxia Modules being loaded multiple times with stack traces like this:

Caused by: org.apache.maven.doxia.siterenderer.RendererException: File '/Users/715508/git/maven/maven-site-plugin/target/it/site-jar/src/site/apt/download.apt.vm' clashes with existing '/Users/715508/git/maven/maven-site-plugin/target/it/site-jar/src/site/apt/download.apt.vm'.
    at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.lambda$checkForDuplicate$0 (DefaultSiteRenderer.java:317)
    at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.checkForDuplicate (DefaultSiteRenderer.java:361)
    at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.checkForDuplicate (DefaultSiteRenderer.java:333)
    at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.addModuleFiles (DefaultSiteRenderer.java:281)
    at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.locateDocumentFiles (DefaultSiteRenderer.java:202)
    at org.apache.maven.plugins.site.render.AbstractSiteRenderingMojo.locateDocuments (AbstractSiteRenderingMojo.java:455)
    at org.apache.maven.plugins.site.render.SiteMojo.renderLocale (SiteMojo.java:151)
    at org.apache.maven.plugins.site.render.SiteMojo.execute (SiteMojo.java:125)

In that case each module is being called multiple times due to it being bound more than once in DefaultParserModuleManager (eclipse-sisu/sisu-project#253).

Once the Doxia modules are loaded from ClassRealm[plugin>org.apache.maven.plugins:maven-project-info-reports-plugin:3.9.0, parent: ClassRealm[plugin>org.apache.maven.plugins:maven-site-plugin:3.22.0-SNAPSHOT, parent: jdk.internal.loader.ClassLoaders$AppClassLoader@c387f44]] and once from ClassRealm[plugin>org.apache.maven.plugins:maven-site-plugin:3.22.0-SNAPSHOT, parent: jdk.internal.loader.ClassLoaders$AppClassLoader@c387f44]