[lworld] RFR: 8374021: [lworld] tools/javac/preview/PreviewAutoSuppress.java compiler.err.is.preview: preview.api.Outer fail

[David Beaumont]

Make test robust against spec version changes.

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Commit messages:
 - unify version number handling
 - simpler version
 - Other test fix

Changes: https://git.openjdk.org/valhalla/pull/2065/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2065&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374021
  Stats: 8 lines in 2 files changed: 3 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/valhalla/pull/2065.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2065/head:pull/2065

PR: https://git.openjdk.org/valhalla/pull/2065