[foreign-memaccess+abi] RFR: Update foreign memory doc [v3]

[Maurizio Cimadamore]

> This patch updates the foreign memory document to reflect the latest API changes in Java 20.
> 
> I've streamlined the document, removed some obsolete sections (as well as sections that didn't seem to add much), and re-ordered the various sections so that the narrative is now easier to follow.

Maurizio Cimadamore has updated the pull request incrementally with two additional commits since the last revision:

 - Update doc/panama_memaccess.md
   
   Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>
 - Update doc/panama_memaccess.md
   
   Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>

-------------

Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/758/files
  - new: https://git.openjdk.org/panama-foreign/pull/758/files/a3eed0fa..7b9a3844

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=758&range=02
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=758&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/758.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/758/head:pull/758

PR: https://git.openjdk.org/panama-foreign/pull/758