RFR: 7903475: Jextract should use new byte-based layout methods

[Maurizio Cimadamore]

This PR tweaks jextract to work with the API changes in the layout API introduced in https://github.com/openjdk/jdk/pull/14013.

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Commit messages:
 - Initial push

Changes: https://git.openjdk.org/jextract/pull/120/files
 Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=120&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903475
  Stats: 97 lines in 28 files changed: 3 ins; 0 del; 94 mod
  Patch: https://git.openjdk.org/jextract/pull/120.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/120/head:pull/120

PR: https://git.openjdk.org/jextract/pull/120