RFR: 8343188: Investigate ways to simplify MemorySegment::ofBuffer [v5]

[Per Minborg]

On Fri, 1 Nov 2024 07:42:34 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> Because heap segments don’t have to be backed by an array.
>
> The reason was what @ExE-Boss mentioned but for me, I am happy with either name. I will update to `heapSegment()`.

The method has been moved into Buffer implementations now.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21764#discussion_r1825544983