[jdk19] RFR: 8289558: Need spec clarification of j.l.foreign.*Layout [v2]

[Maurizio Cimadamore]

> This patch fixes few javadoc issues in the memory layout API.
> The main issues are that `SequenceLayout::flatten` and `SequenceLayout::reshape` still mention failures caused by a lack of size. But that condition is no longer possible in the new API.
> 
> The javadoc of `ValueLayout::arrayElementVarHandle` is suboptimal and can be clarified - UOE is only thrown if the value layout alignment is bigger than its size.
> 
> Finally, the `MemoryLayout::equals` method does not mention value layout carriers.
> 
> The JBS issue associated with this PR mentions also other issues, mostly related to the overly broad visibility of some of the methods in the javadoc (e.g. isPadding). Unfortunately, given the presence of an intermediate, non-public, abstract class, this is what we get from javadoc. Fixing these issues would require a deeper restructuring of the implementation, which would be too riskt at this stage.

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Use pattern match in equals implementation
  Consolidate hashcode

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Changes:
  - all: https://git.openjdk.org/jdk19/pull/98/files
  - new: https://git.openjdk.org/jdk19/pull/98/files/7d993fe2..c5d3f2b3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk19&pr=98&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk19&pr=98&range=00-01

  Stats: 25 lines in 4 files changed: 0 ins; 7 del; 18 mod
  Patch: https://git.openjdk.org/jdk19/pull/98.diff
  Fetch: git fetch https://git.openjdk.org/jdk19 pull/98/head:pull/98

PR: https://git.openjdk.org/jdk19/pull/98