[foreign-memaccess+abi] RFR: 8264386: LibraryLookup should be more friendly with implicit unloading [v2]

[Maurizio Cimadamore]

> Quoting from the PR:
> 
> Dereferencing a segment from a LibraryLookup is possible, in the following form:
> 
> LibraryLookup libLookup = ...
> MemorySegment segment = libLookup.lookup("foo").asSegmentRestricted(....)
> 
> The above code has a problem: there is no link between the produced segment and the original library lookup - meaning that, in principle, it's possible for the library to be unloaded when dereference occurs.
> 
> After having discussed many alternatives with Jorn, the best way to address this conundrum would be to add an overload of `LibraryLookup::lookup` which takes a lyout and returns a segment.
> 
> As part of this change I have also removed the LibraryLookup.Symbol API which seems unnecessary - now you can lookup an address or a segment. Of course, looking up a segment is creating a restricted segment (so it should be treated as unsafe).
> 
> I've added a test to make sure that the new API works as expected.

Maurizio Cimadamore has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Add @NativeAccess annotations and @CallerSensitive check on LibraryLookup::lookup(String, MemoryLayout)
 - Merge branch 'foreign-memaccess+abi' into resourceScope+libraries
 - Initial push

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/480/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/480/files/7bbc6f1a..399d30b3

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=480&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=480&range=00-01

  Stats: 730 lines in 55 files changed: 646 ins; 37 del; 47 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/480.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/480/head:pull/480

PR: https://git.openjdk.java.net/panama-foreign/pull/480