[foreign-jextract] RFR: Jextract changes needed after SystemABI -> ForeignLinker rename

[Jorn Vernee]

Hi,

These are the jextract changes that were needed after renaming SystemABI -> ForeignLinker, and moving layout constants
to the CSupport class. (https://github.com/openjdk/panama-foreign/pull/174)

Jorn

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Commit messages:
 - Jextract changes needed after SystemABI -> ForeignLinker rename

Changes: https://git.openjdk.java.net/panama-foreign/pull/176/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/176/webrev.00
  Stats: 1526 lines in 20 files changed: 16 ins; 30 del; 1480 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/176.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/176/head:pull/176

PR: https://git.openjdk.java.net/panama-foreign/pull/176