RFR: 8312522: Implementation of Foreign Function & Memory API [v13]

[Jorn Vernee]

> This patch contains the implementation of the foreign linker & memory API JEP for Java 22. The initial patch is composed of commits brought over directly from the [panama-foreign repo](https://github.com/openjdk/panama-foreign). The main changes found in this patch come from the following PRs:
> 
> 1. https://github.com/openjdk/panama-foreign/pull/836 Where previous iterations supported converting Java strings to and from native strings in the UTF-8 encoding, we've extended the supported encoding to all the encodings found in the `java.nio.charset.StandardCharsets` class.
> 2. https://github.com/openjdk/panama-foreign/pull/838 We dropped the `MemoryLayout::sequenceLayout` factory method which inferred the size of the sequence to be `Long.MAX_VALUE`, as this led to confusion among clients. A client is now required to explicitly specify the sequence size.
> 3. https://github.com/openjdk/panama-foreign/pull/839 A new API was added: `Linker::canonicalLayouts`, which exposes a map containing the platform-specific mappings of common C type names to memory layouts.
> 4. https://github.com/openjdk/panama-foreign/pull/840 Memory access varhandles, as well as byte offset and slice handles derived from memory layouts, now feature an additional 'base offset' coordinate that is added to the offset computed by the handle. This allows composing these handles with other offset computation strategies that may not be based on the same memory layout. This addresses use-cases where clients are working with 'dynamic' layouts, whose size might not be known statically, such as variable length arrays, or variable size matrices.
> 5. https://github.com/openjdk/panama-foreign/pull/841 Remove this now redundant API. Clients can simply use the difference between the base address of two memory segments.
> 6. https://github.com/openjdk/panama-foreign/pull/845 Disambiguate uses of `SegmentAllocator::allocateArray`, by renaming methods that both allocate + initialize memory segments to `allocateFrom`. (see the original PR for the problematic case)
> 7. https://github.com/openjdk/panama-foreign/pull/846 Improve the documentation for variadic functions.
> 8. https://github.com/openjdk/panama-foreign/pull/849 Several test fixes to make sure the `jdk_foreign` tests can pass on 32-bit machines, taking linux-x86 as a test bed.
> 9. https://github.com/openjdk/panama-foreign/pull/850 Make the linker API required. The `Linker::nativeLinker` method is not longer allowed to throw an `UnsupportedOperationException` on ...

Jorn Vernee has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 34 commits:

 - PPC linker changes
 - Merge branch 'master' into JEP22
 - Paul's review comments
 - Fix typo in doc
   
   Co-authored-by: Paul Sandoz <paul.d.sandoz at googlemail.com>
 - 8315096: Allowed access modes in memory segment should depend on layout alignment
   
   Reviewed-by: psandoz
 - Add missing @implSpec to AddressLayout
   
   Reviewed-by: pminborg
 - Fix misc typos in FFM API javadoc
   
   Reviewed-by: jvernee
 - Clarify javadoc w.r.t. exceptions thrown by a memory access var handle (part two)
   
   Reviewed-by: pminborg
 - Clarify javadoc w.r.t. exceptions thrown by a memory access var handle
   
   Reviewed-by: jvernee
 - remove unsupported linker test
 - ... and 24 more: https://git.openjdk.org/jdk/compare/62a953f4...b8bb791f

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Changes: https://git.openjdk.org/jdk/pull/15103/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15103&range=12
  Stats: 3176 lines in 238 files changed: 1480 ins; 951 del; 745 mod
  Patch: https://git.openjdk.org/jdk/pull/15103.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15103/head:pull/15103

PR: https://git.openjdk.org/jdk/pull/15103