[foreign-abi] [Rev 01] RFR: Tweak API and javadoc for VaList

[Maurizio Cimadamore]

> This is a small patch which fixes some javadoc and API issues in the CSupport.VaList class. Main changes are:
> 
> * CSupport::newVaList has been moved as a static factory in VaList (new name is `make`)
> * Valist::toAddress() renamed to just `address`
> * minor javadoc tweaks to better clarify the distinction between underlying C va list and the Java VaList warpper

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 two additional commits
since the last revision:

 - * Fix issue in javadoc
   * integrate latest changes in StdLibTest
 - Tweak API and javadoc for VaList

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/206/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/206/files/43eca9a3..c4dd1f47

Webrevs:
 - full: https://webrevs.openjdk.java.net/panama-foreign/206/webrev.01
 - incr: https://webrevs.openjdk.java.net/panama-foreign/206/webrev.00-01

  Stats: 75 lines in 5 files changed: 53 ins; 3 del; 19 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/206.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/206/head:pull/206

PR: https://git.openjdk.java.net/panama-foreign/pull/206