[foreign-memaccess+abi] RFR: 8301801: Implement arena-centric API [v2]

[Maurizio Cimadamore]

> This patch implements the API proposal described here:
> 
> https://cr.openjdk.java.net/~mcimadamore/panama/scoped_arenas.html
> 
> The main changes are:
> 
> * Static factories `MemorySegment::allocateNative` are gone;
> * The static factory `SegmentAllocator::nativeAllocator` is also gone;
> * `SegmentScope` moved as nested class in `MemorySegment` (e.g. `MemorySegment.Scope`);
> * Tweak methods accepting `SegmentScope` to accept `Arena` instead;
> * Simplify `Arena` API, by removing predicates (`isCloseable`/`isAccessibleBy`) and by dropping `whileAlive`;
> * Change arena factories to use `of` prefix instead of `open` - and rename `auto()` to `ofAuto()`.
> 
>  The API changes are rather straightforward, but they lead to several shallow test and microbenchmark changes, so the number of affected file is quite big (mostly because of the rename `openConfined` -> `ofConfined`).
> 
> A javadoc of the proposed changes is available here:
> 
> http://cr.openjdk.java.net/~mcimadamore/panama/scoped_arena_interface_lump_predicates/

Maurizio Cimadamore has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:

 - Merge branch 'foreign-memaccess+abi' into arena_centric
 - Fix typo
 - Clarify javadoc for Arena::close
 - Fix linker javadoc
 - Initial push

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Changes: https://git.openjdk.org/panama-foreign/pull/781/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=781&range=01
  Stats: 2279 lines in 132 files changed: 549 ins; 684 del; 1046 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/781.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/781/head:pull/781

PR: https://git.openjdk.org/panama-foreign/pull/781