[foreign-jextract] RFR: Refresh docs to reflect Java 18 API changes [v3]

[Jorn Vernee]

On Tue, 18 Jan 2022 15:23:10 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> This patch updates the memory access and linker docs to reflect the Java 18 API changes.
>
> Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Refresh jextract samples

Marked as reviewed by jvernee (Committer).

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PR: https://git.openjdk.java.net/panama-foreign/pull/630