RFR: 8311591: Add SystemModulesPlugin test case that splits module descriptors with new local variables defined by DedupSetBuilder [v4]

[Christoph]

> Add new test case with sample modules that contains some requires/exports/uses/provides.
> 
> We are just unsure if and how we should add some last step of verificaiton with the extracted and decompiled class.
> 
> Follow up task from https://github.com/openjdk/jdk/pull/14408

Christoph has updated the pull request incrementally with two additional commits since the last revision:

 - Add another required transitive desktop
   
   Assert number of module description generated sub modules
   
   Co-authored-by: Oliver Kopp <kopp.dev at gmail.com>
 - Add copyright header and apply some formatting
   Revert unnecesary CompilerUtil

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15234/files
  - new: https://git.openjdk.org/jdk/pull/15234/files/996c187c..1a2e463e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15234&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15234&range=02-03

  Stats: 189 lines in 9 files changed: 171 ins; 5 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/15234.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15234/head:pull/15234

PR: https://git.openjdk.org/jdk/pull/15234