[lworld] RFR: 8247569: [lworld] Align with spec for <vnew> methods [v5]

[Vicente Romero]

> Value classes constructor should be named <vnew> instead of <init>. This PR can't be pushed without the corresponding support being available on the VM side

Vicente Romero has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:

 - Merge branch 'lworld' into JDK-8247569
 - javac is generating <vnew> method for abstract value classes
 - fixing regression tests
 - removing experimental code
 - 8247569: [lworld] Align with spec for <vnew> methods

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Changes: https://git.openjdk.org/valhalla/pull/771/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=771&range=04
  Stats: 293 lines in 47 files changed: 87 ins; 59 del; 147 mod
  Patch: https://git.openjdk.org/valhalla/pull/771.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/771/head:pull/771

PR: https://git.openjdk.org/valhalla/pull/771