[jdk13u-dev] RFR: 8261483: jdk/dynalink/TypeConverterFactoryMemoryLeakTest.java failed with "AssertionError: Should have GCd a method handle by now"

[Attila Szegedi]

Backporting this to eliminate flakiness of tests. This backport differs in the following ways from the original issue:
* There's no changes to `test/jdk/ProblemList.txt` since the flaky tests were never put on the problem list in this repo.
* Tests with Shenandoah also contain the `-XX:+UnlockExperimentalVMOptions` JVM flag which is still necessary with JDK 13.
* Added the `vm.gc.Serial`, `vm.gc.Parallel`, and `vm.gc.G1` properties to `test/jdk/TEST.ROOT` (in addition to already existing `vm.gc.Z` and `vm.gc.Shenandoah`.) It seems it's the right call to add them, it might help further backported tests in the future.

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Commit messages:
 - 8261483: jdk/dynalink/TypeConverterFactoryMemoryLeakTest.java failed with "AssertionError: Should have GCd a method handle by now"

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/136/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=136&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261483
  Stats: 95 lines in 3 files changed: 74 ins; 8 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/136.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/136/head:pull/136

PR: https://git.openjdk.java.net/jdk13u-dev/pull/136