RFR: 8311172: Classfile.PREVIEW_MINOR_VERSION doesn't match that read from class files

[Chen Liang]

`Classfile.PREVIEW_MINOR_VERSION`, currently -1, is correct when passed to `ClassBuilder::withVersion`, but is incorrect when compared to `ClassModel::minorVersion`, which only sets the bits of 2 lowest bytes to 1 (65536). Discovered when trying to replace an asserted preview minor version with this constant in `PreviewHiddenClass` test porting in #13009, which is currently failing.

Requesting a review from @asotona.

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Commit messages:
 - Include bug ID
 - Fix preview minor version not equal to that obtained from ClassModel

Changes: https://git.openjdk.org/jdk/pull/14731/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14731&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311172
  Stats: 65 lines in 2 files changed: 64 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14731.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14731/head:pull/14731

PR: https://git.openjdk.org/jdk/pull/14731