git: openjdk/panama-foreign: foreign-jextract: Refresh docs to reflect Java 18 API changes

[Maurizio Cimadamore]

Changeset: d8c0fe59
Author:    Maurizio Cimadamore <mcimadamore at openjdk.org>
Date:      2022-01-18 16:10:49 +0000
URL:       https://git.openjdk.java.net/panama-foreign/commit/d8c0fe5918cb1c6c744eb26797ea4fa04142c237

Refresh docs to reflect Java 18 API changes

Reviewed-by: jvernee

! doc/panama_ffi.md
! doc/panama_jextract.md
! doc/panama_memaccess.md