RFR: 8296329: Only compare major versions in jar validator

[Bo Zhang]

As described in [JDK-8296329](https://bugs.openjdk.org/browse/JDK-8296329), previously, the jar validator compare the "version" to validate a multi-release jar. The "version" is a mix of the major and minor version fused into a single int, which might be a negative number with `--enable-preview` - this result in wrong comparison.

This PR fixes it by only comparing major versions.

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Commit messages:
 - 8296329: Only compare major versions in jar validator

Changes: https://git.openjdk.org/jdk/pull/11153/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11153&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296329
  Stats: 118 lines in 3 files changed: 114 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/11153.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11153/head:pull/11153

PR: https://git.openjdk.org/jdk/pull/11153