[lworld] RFR: 8270852: [lworld] bytecodes spinned at runtime should set version to 65535 if preview feature enabled

[Mandy Chung]

This patch prepares for lworld to switch to a preview feature.  Also fix the generation of lambda classes and proxy classes to have `Preload` attribute for value classes (not only primitive classes).

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Commit messages:
 - cleanup import
 - 8270852: [lworld] bytecodes spinned at runtime should set minor_version to 65535 if preview feature enabled

Changes: https://git.openjdk.org/valhalla/pull/779/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=779&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8270852
  Stats: 17 lines in 2 files changed: 9 ins; 3 del; 5 mod
  Patch: https://git.openjdk.org/valhalla/pull/779.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/779/head:pull/779

PR: https://git.openjdk.org/valhalla/pull/779