[foreign-jextract] RFR: 8248710: jextract should not generate Cstring, Cpointer, Cint C-X utility classes

[Athijegannathan Sundararajan]

Cstring, Cpointer, C-X* classes are not generated anymore. Updated tests, samples for the same. Samples updated for
stability issues with foreign-abi crashes as well.

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Commit messages:
 - updating samples for Cpointer, Cstring, C-X* removal and stability.
 - 8248710: jextract should not generate Cstring, Cpointer, Cint C-X utility classes

Changes: https://git.openjdk.java.net/panama-foreign/pull/228/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/228/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248710
  Stats: 857 lines in 14 files changed: 120 ins; 339 del; 398 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/228.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/228/head:pull/228

PR: https://git.openjdk.java.net/panama-foreign/pull/228