[foreign-memaccess+abi] RFR: 8303757: MemorySegment::reinterpret should accept an Arena

[Maurizio Cimadamore]

This patch tweaks the signature of `MemorySegment::reinterpret` to accept `Arena` instead of just `MemorySegment.Scope`. After some more thinking, I realized that the current scope-accepting methods imply that there is an action at a distance: passing an arena scope to `MemorySegment::reinterpret` not only results in new temporal bounds (which is ok, since `Scope` is about that), but also sets confinement constraints too (which is surprising, as a `Scope` doesn't have a notion of confinement).

For this reason, I've dialled back the signature to take an `Arena`. This makes the API more consistent (now "of course" the confinement properties of the returned segment will be specified by the provided arena). It also removes a bit of verbosity at the use site, as doing `arena.scope()` is no longer required.

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Commit messages:
 - Initial push

Changes: https://git.openjdk.org/panama-foreign/pull/812/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=812&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303757
  Stats: 75 lines in 18 files changed: 25 ins; 6 del; 44 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/812.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/812/head:pull/812

PR: https://git.openjdk.org/panama-foreign/pull/812