RFR: Fix jextract/panama to reflect latest API changes

Fri Sep 16 13:59:30 UTC 2022

On Fri, 16 Sep 2022 13:52:27 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> This patch tweaks the jextract implementation to take into account two API changes:
> 
> * `MemorySegment.allocateNative` no longer accepts a session parameter (in all cases we were passing an implicit session, so that's ok)
> * `Linker.methodType` has been moved to `FunctionDescriptor::toMethodType`

Note: I did not fix the samples, but noted that some of them do refer to `MemorySegment.allocateNative` and probably require some fixing.

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PR: https://git.openjdk.org/jextract/pull/72