[lworld] RFR: 8293126: [lworld] follow-up for compiler.err.mod.not.allowed.here

[Vicente Romero]

This PR is providing tests that were missing in the initial PR that fixed [1]. Also we realized that javac is accepting this code as kosher:

    abstract sealed value class SC {}
    non-sealed value class VC extends SC {}

even when concrete value classes are implicitly final, so can't be `non-sealed` at the same time.

[1] https://bugs.openjdk.org/browse/JDK-8293120

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Commit messages:
 - 8293126: [lworld] follow-up for JDK-8293120

Changes: https://git.openjdk.org/valhalla/pull/738/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=738&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293126
  Stats: 50 lines in 2 files changed: 48 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/valhalla/pull/738.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/738/head:pull/738

PR: https://git.openjdk.org/valhalla/pull/738