[foreign-memaccess] RFR: Backport misc changes from foreign-abi

[Paul Sandoz]

On Tue, 31 Mar 2020 13:57:31 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> Hi,
> 
> This patch backports several changes that went into the foreign-abi branch, but which are in retrospect useful to have
> on the memaccess branch, and as part of the memory access API as well.
> These changes include:
> - Replacing ForeignUnsafe with Foreign
> - Adding the `ofNativeUnchecked` method to create unchecked MemorySegments, MemoryAddress::ofLong to forge
>   MemoryAddresses from longs, as well as the Nothing segment and rebase support. Mainly to support going from a `long` to
>   `MemoryAddress`, and also to `MemorySegment` (MA -> long is already covered) The memory layout attributes exposed in
>   the public API (could be interesting to investigate attaching carrier types directly to layouts).
> 
> The MemoryAddress carrier support for VarHandles is left out for now, since the current thinking is that it will be
> dropped and replaced with VarHandle combinators to convert between long and MA instead.
> Thanks,
> Jorn

Marked as reviewed by psandoz (Committer).

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PR: https://git.openjdk.java.net/panama-foreign/pull/77