[foreign-memaccess+abi] RFR: Remove dead code, add tests and fixes [v3]

[Jorn Vernee]

On Tue, 14 Feb 2023 15:39:08 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR suggests removing dead code and addition of some tests. Also, a fix for zero-length mapped segment is added. It is anticipated this special zero-length segment is going to be removed in a separate PR.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Cleanup after comments

Marked as reviewed by jvernee (Committer).

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PR: https://git.openjdk.org/panama-foreign/pull/792