RFR: Tweak jextract to work with latest API changes

Thu Jul 20 12:32:27 UTC 2023

This PR fixes a bunch of issues with jextract that were introduced by the latest changes in the Panama repo:

* All var handles now take an extra offset parameter. This required changes to the libclang generated bindings, as well as changes in the code generated by jextract.
* The name of some allocation factories in SegmentAllocator has changed. This PR fixes jextract to use the right names.
* ValueLayout::arrayElementVarHandle is no longer present

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Commit messages:
 - Tweak jextract to work with latest API changes

Changes: https://git.openjdk.org/jextract/pull/124/files
 Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=124&range=00
  Stats: 41 lines in 15 files changed: 0 ins; 4 del; 37 mod
  Patch: https://git.openjdk.org/jextract/pull/124.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/124/head:pull/124

PR: https://git.openjdk.org/jextract/pull/124