[foreign-jextract] RFR: Update documents to reflect latest API changes

[Maurizio Cimadamore]

Updated both foreign memory and function access docs

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Commit messages:
 - Revert spurious doc changes
 - Update documents to reflect latest API changes

Changes: https://git.openjdk.java.net/panama-foreign/pull/367/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=367&range=00
  Stats: 32 lines in 4 files changed: 4 ins; 0 del; 28 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/367.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/367/head:pull/367

PR: https://git.openjdk.java.net/panama-foreign/pull/367