[foreign-abi] [Rev 01] RFR: 8241504: Expose MemoryLayout annotations/attributes in the public API

[Jorn Vernee]

> Hi,
> 
> This PR exposed MemoryLayout attributes in the public API.
> 
> A summary of the changes:
> - Renamed annotation -> attribute everywhere to avoid confusion with Java language annotations
> - Made sure that annotations were being serialized as part of a MemoryLayout's ConstantDesc, as well as the alignment
>   which was previously left out. (The latter also meant changing PaddingLayout::hasNaturalAlignment to always return
>   `true`, so serializing alignment is skipped for padding). Removed special casing for the abiType attribute. This can
>   now instead be handled through the generic attribute mechanism.
> 
> Thanks,
> Jorn

Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:

  Addressed review comments + added basic tests

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/64/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/64/files/e09a98cc..2d58b86d

Webrevs:
 - full: https://webrevs.openjdk.java.net/panama-foreign/64/webrev.01
 - incr: https://webrevs.openjdk.java.net/panama-foreign/64/webrev.00-01

  Stats: 124 lines in 7 files changed: 96 ins; 16 del; 12 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/64.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/64/head:pull/64

PR: https://git.openjdk.java.net/panama-foreign/pull/64