[foreign-jextract] RFR: Refresh panama documents to reflect API changes [v5]

[Maurizio Cimadamore]

> This patch tweaks the foreign memory access/linker documents to reflect the various changes in the API. Most notable changes are:
> 
> * The name of many static factories (e.g. layouts) has changed
> * We dropped `MemorySegment::allocate` variants which do not accept a scope
> 
> I've also dropped the html version of said documents - since I believe the github rendering to be good enough (and, we refer to the github pages hosting these docs from other places anyway).

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Minor tweaks to ffi doc

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/535/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/535/files/b1efce97..7da9399a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=535&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=535&range=03-04

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/535.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/535/head:pull/535

PR: https://git.openjdk.java.net/panama-foreign/pull/535