RFR: 8256015: Shenandoah: Add missing Shenandoah implementation in WB_isObjectInOldGen

[Roman Kennke]

The test gc/TestReferenceRefersTo.java fails with Shenandoah because of a missing implementation in WB_isObjectInOldGen:

Internal Error (/home/rkennke/src/openjdk/jdk/src/hotspot/share/gc/shared/collectedHeap.hpp:207), pid=511307, tid=511422
assert(kind == heap->kind()) failed: Heap kind 6 should be 1

This is introduced by JDK-8188055. 

Testing: hotspot_gc_shenandoah, tier1+Shenandoah, TestReferenceRefersTo.java

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Commit messages:
 - 8256015: Shenandoah: Add missing Shenandoah implementation in WB_isObjectInOldGen

Changes: https://git.openjdk.java.net/jdk/pull/1111/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1111&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256015
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1111.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1111/head:pull/1111

PR: https://git.openjdk.java.net/jdk/pull/1111