RFR: 8264774: Implementation of Foreign Function and Memory API (Incubator)

[Maurizio Cimadamore]

This PR contains the API and implementation changes for JEP-412 [1]. A more detailed description of such changes, to avoid repetitions during the review process, is included as a separate comment.

[1] - https://openjdk.java.net/jeps/412

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Commit messages:
 - Add linker test excludes for x86 and other platforms which do not support `CLinker`
 - Integrate latest API tweaks
 - Fix x86 build
 - Fix `TestLinkToNativeRBP`
 - Initial push

Changes: https://git.openjdk.java.net/jdk/pull/3699/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3699&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264774
  Stats: 14083 lines in 213 files changed: 8502 ins; 3605 del; 1976 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3699.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3699/head:pull/3699

PR: https://git.openjdk.java.net/jdk/pull/3699