[foreign-memaccess] [Rev 01] RFR: JDK-8243284: Remove Foreign class

[Maurizio Cimadamore]

> The Foreign class is currently used for 3 methods:
> 
> * withSize, which takes an unchecked address and gives it a size
> * asUnconfined, which takes an existing segment and turns it into an unconfined segment
> * asMallocSegment, which takes an unchecked address and converts that into a segment which can be closed, and where
>   closed is mapped into "free"
> 
> This patch replaces all these with this method:
> 
> static MemorySegment ofNativeUnsafe(MemoryAddress addr, long bytesSize, Thread owner, AutoCloseable cleanup, Object
> attachment)
> Which is then moved directly into MemorySegment - so that we can garbage-collect the Foreign class.
> 
> I've also made some changes on the JDK property - new name is simply "jdk.foreign" and I now made sure that it cannot
> be bypassed with a simple static initializer.

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

  * simplified API to take Runnable instead of AutoCloseable
  * renamed all occurrences of "unsafe" with "restricted" (e.g. as in "restricted foreign")
  * cleaned up the code which performs the restricted access check

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/122/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/122/files/286c8d07..10b7929a

Webrevs:
 - full: https://webrevs.openjdk.java.net/panama-foreign/122/webrev.01
 - incr: https://webrevs.openjdk.java.net/panama-foreign/122/webrev.00-01

  Stats: 59 lines in 7 files changed: 1 ins; 28 del; 30 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/122.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/122/head:pull/122

PR: https://git.openjdk.java.net/panama-foreign/pull/122