[foreign-abi] [Rev 04] 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 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 17 additional commits since
the last revision:

 - Merge branch 'Attributes' of https://github.com/JornVernee/panama-foreign into Attributes
 - Don't filter by type when looking up layout attributes, and instead fail with a CCE by casting directly if the type is
   incorrect, to avoid silent errors.
 - Update src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/SystemABI.java
   
   Co-Authored-By: Maurizio Cimadamore <54672762+mcimadamore at users.noreply.github.com>
 - Remove ML::attribute(String, Class) helper method.
 - Addressed review comments + added basic tests
 - Removed trailing whitespace
 - Clean up diff
 - Removed abiType, added type-casting helper for attribute
 - Rename annotations to attributes, and expose them in the public API.
 - Merge branch 'Attributes' of https://github.com/JornVernee/panama-foreign into Attributes
 - Remove ML::attribute(String, Class) helper method.
 - Update src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/SystemABI.java
   
   Co-Authored-By: Maurizio Cimadamore <54672762+mcimadamore at users.noreply.github.com>
 - Addressed review comments + added basic tests
 - Removed trailing whitespace
 - Clean up diff
 - Removed abiType, added type-casting helper for attribute
 - Rename annotations to attributes, and expose them in the public API.

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/64/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/64/files/d3baa351..19e5560e

Webrevs:
 - full: https://webrevs.openjdk.java.net/panama-foreign/64/webrev.04
 - incr: https://webrevs.openjdk.java.net/panama-foreign/64/webrev.03-04

  Stats: 405 lines in 12 files changed: 392 ins; 4 del; 9 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