RFR: 8275063: Implementation of Foreign Function & Memory API (Second incubator) [v18]

[Maurizio Cimadamore]

> This PR contains the API and implementation changes for JEP-419 [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/419

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  * Add two new CLinker static methods to compute upcall/downcall method types
  * Clarify section on CLinker downcall type
  * Add section on CLinker safety guarantees

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5907/files
  - new: https://git.openjdk.java.net/jdk/pull/5907/files/b9432473..ce561e1f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5907&range=17
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5907&range=16-17

  Stats: 79 lines in 3 files changed: 47 ins; 17 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5907.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5907/head:pull/5907

PR: https://git.openjdk.java.net/jdk/pull/5907