[foreign-memaccess] RFR: 8249790: Add Addressable abstraction [v3]

[Maurizio Cimadamore]

> This patch adds a new entity in the Foreign Memory Access API, namely `Addressable`. This is a simple functional
> interface which is implemented by all the entities which can be mapped onto a `MemoryAddress`. For now, only
> `MemoryAddress` and `MemorySegment` implements it (but on the foreign-abi branch we will repeat the exercise and add
> more implementations).

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

  Add copyright
  Fix typo in Addressable javadoc

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/252/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/252/files/efceeed7..793227bf

Webrevs:
 - full: https://webrevs.openjdk.java.net/panama-foreign/252/webrev.02
 - incr: https://webrevs.openjdk.java.net/panama-foreign/252/webrev.01-02

  Stats: 26 lines in 1 file changed: 25 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/252.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/252/head:pull/252

PR: https://git.openjdk.java.net/panama-foreign/pull/252