RFR: 8357531: The `SegmentBulkOperations::fill` method can be improved using overlaps [v3]

[Per Minborg]

> This PR builds on a concept John Rose told me about some time ago. Instead of combining memory operations of various sizes, a single large and skewed memory operation can be made to clean up the tail of remaining bytes.
> 
> This has the effect of simplifying and shortening the code. The number of branches to evaluate is reduced.
> 
> It should be noted that the performance of the fill operation affects the allocation of new segments (as they are zeroed out before being returned to the client code).

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

  Add case for long operations and break out methods

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/25383/files
  - new: https://git.openjdk.org/jdk/pull/25383/files/9e0d67ec..65c88fba

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25383&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25383&range=01-02

  Stats: 54 lines in 1 file changed: 32 ins; 17 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/25383.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25383/head:pull/25383

PR: https://git.openjdk.org/jdk/pull/25383