[jdk11u-dev] RFR: 8251132: make main classes public in vmTestbase/jit tests

[Goetz Lindenmaier]

This test cleanup is a clean backport and simplifies follow-up backports.

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Commit messages:
 - Backport 65577cf58a3b3221ca4a84e22ae0fc386dbc4c1e

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/755/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=755&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251132
  Stats: 498 lines in 138 files changed: 0 ins; 132 del; 366 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/755.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/755/head:pull/755

PR: https://git.openjdk.java.net/jdk11u-dev/pull/755