RFR: 8365017: The SegmentBulkOperations::copy method can be improved using overlaps [v8]

[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:

  Break out the default branch

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26672/files
  - new: https://git.openjdk.org/jdk/pull/26672/files/1a1606e2..e05c8370

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26672&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26672&range=06-07

  Stats: 18 lines in 1 file changed: 8 ins; 4 del; 6 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