RFR: 8277924: Small tweaks to foreign function and memory API [v5]

[Maurizio Cimadamore]

> Following integration of the second incubator of the foreign function and memory API [1], we detected few divergences between the contents of the jdk repo and the panama repo:
> 
> * the name of some of the `FunctionDescriptor` wither methods is different (e.g. `withAppendedLayoutArguments` vs. `appendLayoutArguments`), as it has been simplified and improved following a change that was not incorporated in [1].
> 
> * TestUpcall does not execute all the test combinations, because of an issue in the jtreg header (also fixed in the panama repo)
> 
> * Addressing some feedback, we would like to bring back alignment to JAVA_INT layout constants (and related constants). 
> 
> Javadoc: http://cr.openjdk.java.net/~mcimadamore/8277924/v1/javadoc/jdk/incubator/foreign/package-summary.html
> Specdiff: http://cr.openjdk.java.net/~mcimadamore/8277924/v1/spec_diff/overview-summary.html
> 
> [1] - #5907

Maurizio Cimadamore has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 12 additional commits since the last revision:

 - Revert test change
 - Merge branch 'master' into value_layout_align
 - Simplify FunctionDescriptor::insertArgumentLayouts
 - Drop changes to alignment of layout constants
 - Simplify logic to access package-private method in ValueLayout
 - Update src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/ValueLayout.java
   
   Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>
 - Further tweak to javadoc of layout constants
 - Wrong alignment constraints in ValueLayout constants javadoc
 - Tweak javadoc
 - Fix jtreg header on TestUpcall
 - ... and 2 more: https://git.openjdk.java.net/jdk/compare/26afe572...f3f78190

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6589/files
  - new: https://git.openjdk.java.net/jdk/pull/6589/files/c305199c..f3f78190

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6589&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6589&range=03-04

  Stats: 7127 lines in 257 files changed: 4342 ins; 1547 del; 1238 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6589.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6589/head:pull/6589

PR: https://git.openjdk.java.net/jdk/pull/6589