RFR: 8330821: Rename UnsafeCopyMemory

[Scott Gibbons]

Renaming UnsafeCopyMemory to UnsafeMemoryAccess since this class is now being used for Unsafe::setMemory.  This is a pure rename only.

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Commit messages:
 - Rename UnsafeCopyMemory to UnsafeMemoryAccess

Changes: https://git.openjdk.org/jdk/pull/18889/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18889&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330821
  Stats: 159 lines in 18 files changed: 0 ins; 0 del; 159 mod
  Patch: https://git.openjdk.org/jdk/pull/18889.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18889/head:pull/18889

PR: https://git.openjdk.org/jdk/pull/18889