RFR: 8365017: The SegmentBulkOperations::copy method can be improved using overlaps [v2]

[Per Minborg]

> This PR proposes to use overlapping memory areas in `SegmentBulkOperations::copy`, similar to what is proposed for `SegmentBulkOperations::fill` in https://github.com/openjdk/jdk/pull/25383.
> 
> This PR passes `tier1`, `tier2`, and `tier3`testing on multiple platforms.

Per Minborg has updated the pull request incrementally with one additional commit since the last revision:

  Optimize copy for certain lengths

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26672/files
  - new: https://git.openjdk.org/jdk/pull/26672/files/7d4c7881..b60832ce

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26672&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26672&range=00-01

  Stats: 11 lines in 1 file changed: 7 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/26672.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26672/head:pull/26672

PR: https://git.openjdk.org/jdk/pull/26672