[foreign-memaccess+abi] RFR: Revert SegmentAllocator API changes

[Per Minborg]

On Thu, 17 Aug 2023 17:01:44 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> This patch reverts the changes to the `implSpec` of the various default methods in `SegmentAllocator`.
> We have realized that the changes there are irrelevant. What matters in order to get to optimal peak performance is that `SegmentAllocator::copyArrayWithSwapIfNeeded` is force-inlined.
> 
> The segment allocator test is also reverted to its former self.

test/jdk/java/foreign/TestSegmentAllocators.java line 194:

> 192:         SegmentAllocator allocator = new SegmentAllocator() {
> 193:             @Override
> 194: 

Extraneous line

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PR Review Comment: https://git.openjdk.org/panama-foreign/pull/868#discussion_r1298068448