[foreign-abi] [Rev 01] RFR: JDK-8242061: AllocationScope is too general

[Maurizio Cimadamore]

> This patch restricts allocation scope to work only on native allocations. This restriction allows us to lift the size
> limitations from unbounded allocation scopes (as we can always fallback on a MemorySegment.allocateNative which
> guarantees correct alignment).

Maurizio Cimadamore has updated the pull request incrementally with two additional commits since the last revision:

 - Tweak test to also check alignment of allocatd blocks
 - * Fix allocation limit for case where standalone segment is created (limit has to take into account worst case with
     alignment)
   * Add test for big allocations

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Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/93/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/93/files/2f9b3c09..393b6f11

Webrevs:
 - full: https://webrevs.openjdk.java.net/panama-foreign/93/webrev.01
 - incr: https://webrevs.openjdk.java.net/panama-foreign/93/webrev.00-01

  Stats: 26 lines in 4 files changed: 15 ins; 2 del; 9 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/93.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/93/head:pull/93

PR: https://git.openjdk.java.net/panama-foreign/pull/93