Bump PMD to 7.8.0 and spotbugs to 4.8.6

[Jimver]

• Bump the pmd dependency from 6.0.0 to the latest version 7.8.0.
• This is needed in particular for Java 21 support. See https://pmd.github.io/pmd/pmd_languages_java.html
• Changed the PmdProcessor to be compatible with the new PMD 7.8.0 version.
• For PMD we now just use the PmdAnalysis class to perform the PMD checks based on our PMDConfiguration, giving back the Report.
• Therefore, we don't need to do our own manual CollectorRenderer anymore, so that is now removed.
• Note that the rulesets have changed to be category based in the test properties, this will also need to be updated in the properties of end users.
• Bump the spotbugs dependency from 4.2.0 to the latest version 4.8.6.
• This is needed for Java 21 support, see spotbugs releasenotes: https://github.com/spotbugs/spotbugs/releases/tag/4.8.0
• Need to exclude logback from spotbugs since it's a newer version compiled with class version 55 (we are still on class version 52 with JDK 1.8).
• The PMD and spotbugs bumps are done in unison as they both use the saxon dependency.

[Jimver]

Fixes #262