Describe the PR

This is my own attempt to this issue...

Things to think about, stuff that is not ready

• should we really rename auxclasspath to analysisclasspath? What is the correct name? Auxclasspath is older, but IMHO AnalysisClasspath sounds better
• should we introduce now AnalysisClasspath or keep it as a simple String in PMDConfiguration?
• When should we validate the provided auxclasspath (e.g. do the provided paths exist, etc.). We probably should do this not here, but in [java] Report missing classes during analysis #5064 .
• documentation / api doc and tests
  • especially the usage scenarios you mention in the description of [java] Fix #4953: Deprecate methods of PMDConfiguration that use ClassLoader #6312 (e.g. reusing PMDConfiguration)
• This is API compatible, but heavily changes the semantics of PMDConfiguration - e.g. the sequence of the calls prependAuxclasspath, getClassloader.getURLs() doesn't work anymore (we used that in unit tests). Is this a problem?
  • In summary I think, the main culprit is that PMDConfiguration is more than data
• Were should the logic be placed to interpret the classpath string provided to PMD? I've extracted it into separately used methods in ClasspathClassloader, but it maybe belongs to AnalysisClasspath
• Maybe the performance problem for our rule unit tests could be solved in a more elegant way - ideally some solution, that we can keep (and no temporary solution)
• commit messages here need to be redone
• ...

Some ideas on how to approach part of this and make this change even smaller:

• first refactor ClasspathClassloader to define, where the logic for parsing a string into URLs belong
• refactor Analysis Cache / Fingerprinter to not use URLs, if possible. If at all, we should use URIs.

Related issues

• Fix [core] Deprecate PMDConfiguration#setClassloader and #getClassloader #4953

Ready?

• Added unit tests for fixed bug/feature
• Passing all unit tests
• Complete build ./mvnw clean verify passes (checked automatically by github actions)
• Added (in-code) documentation (if needed)