RFR: 8312522: Implementation of Foreign Function & Memory API

[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 unsupported platforms. All tests are turned on by default, instead of being skipped when the linker is not present.
10. https://github.com/openjdk/panama-foreign/pull/851 Minor code tweaks to ensure the JIT can constant fold through native access checks if the accessing class is statically known (see commit/original PR for changes).
11. https://github.com/openjdk/panama-foreign/pull/853 Remove all the `@PreviewFeature` annotations from the API. Update all `@since` tags in the Javadoc to `@since 22` (per [JEP 12](https://bugs.openjdk.org/browse/JDK-8195734)). Update tests and benchmarks to no longer build and run using `--enable-preview` (or the `@enablePreview` jtreg tag).

I want to call out in particular that this patch finalizes the FFM API (by moving it out of preview), and requires all JDK implementations to implement it. Most ports already have full FFM API support. The ones that are missing are: s390 ([currently under review](https://github.com/openjdk/jdk/pull/14801)), windows-x86 (deprecated for removal), and linux-86 & arm32 (which can both be implemented using the fallback linker [1](https://github.com/openjdk/panama-foreign/pull/770) [2](https://mail.openjdk.org/pipermail/porters-dev/2023-March/000753.html)).

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Commit messages:
 - use immutable map for fallback linker canonical layouts
 - 8313265: Move the FFM API out of preview
 - 8313005: Ensure native access check can fold away
 - 8312981: Make the linker API required
 - 8312615: Ensure jdk_foreign tests pass on linux-x86
 - 8312186: TestStringEncodingFails for UTF-32
 - 8312059: Clarify the documention for variadic functions
 - 8311533: SegmentAllocator::allocateArray call can be ambiguous
 - 8310893: VarHandleTestExact fails
 - 8310820: Remove MemorySegment::segmentOffset
 - ... and 4 more: https://git.openjdk.org/jdk/compare/6fca2898...b0a1abaf

Changes: https://git.openjdk.org/jdk/pull/15103/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15103&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8312522
  Stats: 2444 lines in 224 files changed: 1084 ins; 721 del; 639 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