[lworld] RFR: 8224057: [lworld] a hidden value class can't have <vnew> static factory method

[Mandy Chung]

A hidden class has no name.  Rather than declaring a "<vnew>" method, a hidden value class will have to provide a different mechanism to create value instances.

This PR adds a test to verify that.

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Commit messages:
 - 8224057: [lworld] a hidden value class can't have <vnew> static factory method

Changes: https://git.openjdk.org/valhalla/pull/798/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=798&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8224057
  Stats: 221 lines in 3 files changed: 219 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/valhalla/pull/798.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/798/head:pull/798

PR: https://git.openjdk.org/valhalla/pull/798