RFR: 8295104: Break VarHandle tests into separate @test to reduce test execution time

[Mandy Chung]

This separates `@run` into its own `@test` that they can be run concurrently.

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Commit messages:
 - 8295104: Break VarHandle tests into separate @test to reduce test execution time

Changes: https://git.openjdk.org/jdk/pull/10641/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10641&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295104
  Stats: 176 lines in 17 files changed: 176 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10641.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10641/head:pull/10641

PR: https://git.openjdk.org/jdk/pull/10641