[foreign-abi] RFR: 8254156: Simplify ABI classification logic

[Jorn Vernee]

On Wed, 7 Oct 2020 11:39:50 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> This patch reverts recent changes to introduce a public CValueLayout class; the realization here is that, after all,
> CValueLayout exposes a public `Type` enum which is used by ABI classification. So, instead of using subclassing (which
> is messy and tedious with immutable data structures with covariant overrides), let's just double down on layout
> attributes, get rid of CValueLayout and simply expose the Type enum (now renamed to TypeKind).

Marked as reviewed by jvernee (Committer).

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PR: https://git.openjdk.java.net/panama-foreign/pull/371