[foreign-memaccess+abi] RFR: Break out functionality to internal class

[Maurizio Cimadamore]

On Mon, 19 Sep 2022 13:30:51 GMT, Per Minborg <duke at openjdk.org> wrote:

> This PR moves some of the internal concerns from `MemorySegment` to the internal `AbstractMemorySegmentImpl`.
> 
> Also, some renaming of static fields.

src/java.base/share/classes/java/lang/foreign/MemoryLayout.java line 594:

> 592:     boolean equals(Object other);
> 593: 
> 594:     /**

public API changes, if needed, require separate PR for clarity

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PR: https://git.openjdk.org/panama-foreign/pull/727