RFR: 8324873: [lworld] implementation of value classes construction

[Vicente Romero]

implementing value classes construction approach as per JEP-401. There is also a bit of an off-road incursion into jdeps removing references to Q-descriptors, probably should have gone in another patch but the changes are kind of small anyways

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Commit messages:
 - changes to jdeps
 - allowing assignment to fields before super
 - Merge branch 'jep_401_javac' into JDK-8324873
 - Merge branch 'jep_401_javac' into JDK-8324873
 - Merge branch 'jep_401_javac' into JDK-8324873
 - 8324873: [lworld] implementation of value classes construction

Changes: https://git.openjdk.org/valhalla/pull/990/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=990&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324873
  Stats: 161 lines in 21 files changed: 38 ins; 86 del; 37 mod
  Patch: https://git.openjdk.org/valhalla/pull/990.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/990/head:pull/990

PR: https://git.openjdk.org/valhalla/pull/990