[jdk11u-dev] RFR: 8210700: Clean up JNI_ENV_ARG and factorize the macros for vmTestbase/jvmti/unit tests

[Goetz Lindenmaier]

I backport this for parity with 11.0.14-oracle.

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Commit messages:
 - Backport bdf78f557a3273f2a628badf19439b220318f73c

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/648/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=648&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8210700
  Stats: 848 lines in 29 files changed: 1 ins; 592 del; 255 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/648.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/648/head:pull/648

PR: https://git.openjdk.java.net/jdk11u-dev/pull/648