RFR: 8256670: Zero: enable compressed oops support back

[Aleksey Shipilev]

UseCompressedOops was disabled for C++ interpreter by JDK-6909153, and it eventually morphed to disabled UseCompressedOops for all Zero configurations. I see nothing that actually prevents Zero from using compressed oops: all local/stack operands are always unpacked (like they are in non-interpreted modes), all heap accesses are calling into utility methods that handle compressed oops, there are no raw accesses to oops anywhere.

Additional testing:
 - [x] Ad-hoc benchmark tests
 - [x] `hotspot_gc_shenandoah` with Zero, now passing compressed oops tests

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Commit messages:
 - 8256670: Zero: enable compressed oops support back

Changes: https://git.openjdk.java.net/jdk/pull/1320/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1320&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256670
  Stats: 8 lines in 1 file changed: 0 ins; 8 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1320.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1320/head:pull/1320

PR: https://git.openjdk.java.net/jdk/pull/1320