[lworld] RFR: JDK-8251986: [lworld] implement Class::valueType and Class::referenceType in Java

[Mandy Chung]

Now that javac generates the reference projection class as a sealed type, this patch reimplements
`Class::valueType` and `Class::referenceType` in Java.  VM no longer has any knowledge of
the value projection type and reference projection type.

This patch includes a temporary workaround to disable the preview feature check for sealed types
because inline types are not (yet) a preview feature in valhalla repo.  This workaround should be
removed when it's time to make inline class a preview feature.

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Commit messages:
 - supports_sealed_types checks only the major version
 - remove unused import
 - disable preview feature check for sealed types
 - Merge branch 'lworld' of https://github.com/openjdk/valhalla into lworld
 - implement Class::referenceType and Class::valueType in Java

Changes: https://git.openjdk.java.net/valhalla/pull/152/files
 Webrev: https://webrevs.openjdk.java.net/valhalla/152/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251986
  Stats: 157 lines in 5 files changed: 83 ins; 54 del; 20 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/152.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/152/head:pull/152

PR: https://git.openjdk.java.net/valhalla/pull/152