RFR: 8329469: Generational ZGC: Move the methods forwarding_[index|find|insert] from zRelocate.cpp to ZForwarding

[Guoxiong Li]

Hi all,

This patch moves the methods `zRelocate.cpp/forwarding_[index|find|insert]`  from the file `zRelocate.cpp` to the class `ZForwarding`.  The first parameter of the methods `zRelocate.cpp/forwarding_[index|find|insert]` is always `ZForwarding*`. These methods should be placed in the class `ZForwarding` so that the first parameter `ZForwarding*` can be added by the compiler and then it can improve the encapsulation.

But the non-generational ZGC can't make such a move because the method signatures may be duplicate.

The test `make test-tier1_gc` passed locally. Thanks for taking the time to review.

Best Regards,
-- Guoxiong

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Commit messages:
 - Move methods about ZForwarding.

Changes: https://git.openjdk.org/jdk/pull/18579/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18579&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329469
  Stats: 83 lines in 3 files changed: 39 ins; 34 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/18579.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18579/head:pull/18579

PR: https://git.openjdk.org/jdk/pull/18579