RFR: 8255733: [type-restrictions] Enhance Javac to help with generation of test files for type restrictions experiments

[Srikanth Adayapalam]

Added option -XDflattenWithErasure to generate class files without the RestrictedField attribute

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Commit messages:
 - 8255733: [type-restrictions] Enhance Javac to help with generation of test files for type restrictions experiments

Changes: https://git.openjdk.java.net/valhalla/pull/251/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=251&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255733
  Stats: 10 lines in 3 files changed: 6 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/251.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/251/head:pull/251

PR: https://git.openjdk.java.net/valhalla/pull/251