[lworld] RFR: 8288644: [lw4] Unable to extend a separately compiled abstract value class

[Srikanth Adayapalam]

Lower constructors in abstract value classes into void <init> methods and in concrete value classes into static factory methods.

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Commit messages:
 - 8288644: [lw4] Unable to extend a separately compiled abstract value class

Changes: https://git.openjdk.org/valhalla/pull/717/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=717&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288644
  Stats: 70 lines in 6 files changed: 46 ins; 1 del; 23 mod
  Patch: https://git.openjdk.org/valhalla/pull/717.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/717/head:pull/717

PR: https://git.openjdk.org/valhalla/pull/717