[foreign-memaccess] [Rev 01] RFR: 8240874: Add finer-grained access control for memory segments

[Maurizio Cimadamore]

> This patch adds a finer-grained access control for memory segments; instead of the ad-hoc `MemorySegment::asReadOnly`,
> we now support a more complete `MemorySegment::withAccessModes`, where access modes is an int mask.
> Supported access modes are `READ`, `WRITE`, `CLOSE` and `ACQUIRE`, which gives much more freedom to clients when it
> comes to create restricted views (I've added a new section on that in the MemorySegment toplevel javadoc).
> I also did some minor changes, mostly to get rid of confinement restrictions where such restrictions were not needed
> (e.g. `MemorySegment::asSlice`).

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

  * add hasAccessModes() predicate
  * fix data provider

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/45/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/45/files/083e0334..8287f1bc

Webrevs:
 - full: https://webrevs.openjdk.java.net/panama-foreign/45/webrev.01
 - incr: https://webrevs.openjdk.java.net/panama-foreign/45/webrev.00-01

  Stats: 19 lines in 4 files changed: 13 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/45.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/45/head:pull/45

PR: https://git.openjdk.java.net/panama-foreign/pull/45