RFR: 8311591: Add SystemModulesPlugin test case that splits module descriptors with new local variables defined by DedupSetBuilder [v8]

[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 one additional commit since the last revision:

  remove obsolete constant

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15234/files
  - new: https://git.openjdk.org/jdk/pull/15234/files/2bcdd2fc..94fcd8d1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15234&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15234&range=06-07

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 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