[foreign-jextract] RFR: Refresh panama documents to reflect API changes

[Maurizio Cimadamore]

This change updates the memory access/linker markdown documents, to reflect the latest API changes described in [1].

[1] - https://inside.java/2021/09/16/finalizing-the-foreign-apis/

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Commit messages:
 - Merge branch 'foreign-jextract' into update_docs
 - Add footnote on invokeExact and Addressable
 - Update panama_ffi.md
 - Update panama_memaccess.md
 - Refresh memory access and linker docs to reflect API changes
 - Address review comments
 - Remove commented lines
 - Merge branch 'foreign-jextract' into foreign-finalize+jextract
 - Tweak test after removal of MemoryAddress::freeMemory
 - Add/fix copyright headers
 - ... and 11 more: https://git.openjdk.java.net/panama-foreign/compare/80e0d4b9...3f42f5d6

Changes: https://git.openjdk.java.net/panama-foreign/pull/578/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=578&range=00
  Stats: 223 lines in 2 files changed: 25 ins; 51 del; 147 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/578.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/578/head:pull/578

PR: https://git.openjdk.java.net/panama-foreign/pull/578