RFR: 8319709: Make GrowableArrayCHeap copyable

[Johan Sjölen]

Hi,

Please consider this code change which makes `GrowableArrayCHeap` copyable. The resulting copy does not share its data array with the original.

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Commit messages:
 - Rename testing struct
 - Copy assignment and copy constructor for GrowableArrayCHeap

Changes: https://git.openjdk.org/jdk/pull/16559/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16559&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319709
  Stats: 88 lines in 2 files changed: 85 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16559.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16559/head:pull/16559

PR: https://git.openjdk.org/jdk/pull/16559