RFR: 8237359: Clean up Binding

[Jorn Vernee]

Continuation of: https://mail.openjdk.java.net/pipermail/panama-dev/2020-February/007417.html

> Hi,
> 
> Please review the following patch that does a few cleanups of the 
> Binding class implementation:
> - Adds javadoc
> - Uses static factory methods instead of raw constructors. This allows 
> returning singletons for some of the operators for instance.
> - Constructing a COPY_BUFFER binding now requires a MemoryLayout, 
> instead of a separate size & alignment. This was easier given the use-cases.
> - Binding.AllocateBuffer renamed to Binding.Allocate (since we already 
> had Copy as well).
> - BoxAddress renamed to ConvertAddress, as a more general name to 
> describe the boxing & unboxing that can occur. Suggested by Maurizio.
> 
> Webrev: 
> http://cr.openjdk.java.net/~jvernee/panama/webrevs/cleanup_bindings/webrev.00/
> Bugs: https://bugs.openjdk.java.net/browse/JDK-8237359, 
> https://bugs.openjdk.java.net/browse/JDK-8238227, 
> https://bugs.openjdk.java.net/browse/JDK-8238235
> 
> This patch take care of several smaller issues all at once. It applies 
> on top of the JDK-8237360 patch.
> 
> Thanks,
> Jorn

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

Commits:
 - 40562472: Fix whitespace errors
 - a4070e24: Use '->' switch
 - d215ddb6: Add Binding.Builder
 - 523e230c: Add enum for Tags
 - 048077ef: Clean up Binding

Changes: https://git.openjdk.java.net/panama-foreign/pull/12/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/12/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8237359
  Stats: 681 lines in 9 files changed: 280 ins; 14 del; 387 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/12.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/12/head:pull/12

PR: https://git.openjdk.java.net/panama-foreign/pull/12