[jdk11u-dev] RFR: 8210194: [TESTBUG] jvmti_FollowRefObjects.cpp missing initializer for member _jvmtiHeapCallbacks::heap_reference_callback

[Aleksey Shipilev]

Clean backport to soothe compilation warnings in 11.0.14 after [JDK-8209611](https://bugs.openjdk.java.net/browse/JDK-8209611) backport. This affects one of our CIs.

Additional testing:
 - [x] Linux x86_64 fastdebug `vmTestbase_nsk_jvmti` still passes

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Commit messages:
 - Backport 3c135ae7055aa7371c0ac7f88fe3f30c0d3f86f0

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/761/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=761&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8210194
  Stats: 4 lines in 4 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/761.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/761/head:pull/761

PR: https://git.openjdk.java.net/jdk11u-dev/pull/761