[foreign-memaccess+abi] RFR: 8291826: Rework MemoryLayout Sealed Hierarchy [v4]

[Per Minborg]

> This PR is a significant refactor of the `MemoryLayout` sealed hierarchy and whose purpose is described more in detail in  https://bugs.openjdk.org/browse/JDK-8291826. In short, the main purpose is to allow pattern matching.
> 
> The objective of the PR is to fix the issues described above while retaining as much API compatibility as possible with the pre-PR API. No changes were needed in any of the existing tests for example.
> 
> The old sealed hierarchy prevented pattern matching with totality from being used and implied a number of other problems as illustrated in the picture below:
> 
> ![graphviz (33)](https://user-images.githubusercontent.com/7457876/185412743-febeb3cf-aebc-4e2e-b78f-3b8ef87b0510.png)
> 
> Red nodes cannot be used in pattern matching. Light red nodes are implementations that are visible in the API. White nodes are interfaces.
> 
> After this PR has been integrated, an improved sealed hierarchy will exist as depicted here:
> 
> ![graphviz (34)](https://user-images.githubusercontent.com/7457876/185413448-8435b23f-5ac4-4999-8b0a-0d6051a0d9be.png)
> 
> Gray "Impl" nodes are internal and not exported by the `java.base` module. White nodes are interfaces.
> 
> Below, the "Principal Totalities" for the new API are outlined:
> 
> 
> var v0 = switch (memoryLayout) {
>   case MemoryLayout ml -> 0;
> };
> var v1 = switch (memoryLayout) {
>   case GroupLayout gl -> 0;
>   case PaddingLayout pl -> 0; // leaf
>   case SequenceLayout sl -> 0; // leaf
>   case ValueLayout vl -> 0;
> };
> var v2 = switch (memoryLayout) {
>   case PaddingLayout pl -> 0; // leaf
>   case SequenceLayout sl -> 0; // leaf
>   case ValueLayout vl -> 0;
>   case StructLayout sl -> 0; // leaf
>   case UnionLayout ul -> 0; // leaf
> };
> var v3 = switch (memoryLayout) {
>   case PaddingLayout pl -> 0; // leaf
>   case SequenceLayout sl -> 0; // leaf
>   case StructLayout sl -> 0; // leaf
>   case UnionLayout ul -> 0; // leaf
>   case OfAddress oa -> 0; // leaf
>   case OfBoolean ob -> 0; // leaf
>   case OfByte ob -> 0; // leaf
>   case OfChar oc -> 0; // leaf
>   case OfDouble od -> 0; // leaf
>   case OfFloat of -> 0; // leaf
>   case OfInt oi -> 0; // leaf
>   case OfLong ol -> 0; // leaf
>   case OfShort os -> 0; // leaf
> };
> var v4 = switch (memoryLayout) {
>   case GroupLayout gl -> 0;
>   case PaddingLayout pl -> 0; // leaf
>   case SequenceLayout sl -> 0; // leaf
>   case OfAddress oa -> 0; // leaf
>   case OfBoolean ob -> 0; // leaf
>   case OfByte ob -> 0; // leaf
>   case OfChar oc -> 0; // leaf
>   case OfDouble od -> 0; // leaf
>   case OfFloat of -> 0; // leaf
>   case OfInt oi -> 0; // leaf
>   case OfLong ol -> 0; // leaf
>   case OfShort os -> 0; // leaf
> };
> 
> 
> 
>  Additional improvements can be made later in a separate PR, including removing/improving some of the internal abstract classes.

Per Minborg has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:

 - Merge foreign-memaccess+abi
 - Update after comments
 - Update src/java.base/share/classes/java/lang/foreign/MemoryLayout.java
   
   Co-authored-by: Paul Sandoz <paul.d.sandoz at googlemail.com>
 - Add tests and update return types
 - Rework MemoryLayout Sealed Hierarchy

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

Changes: https://git.openjdk.org/panama-foreign/pull/710/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=710&range=03
  Stats: 2672 lines in 19 files changed: 1759 ins; 730 del; 183 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/710.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/710/head:pull/710

PR: https://git.openjdk.org/panama-foreign/pull/710