[foreign-jextract] RFR: 8258405: functional interfaces are not generated for struct fields/global variables with function pointers

[Athijegannathan Sundararajan]

generating functional interfaces for globals and function pointer struct members

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Commit messages:
 - 8258405: functional interfaces are not generated for struct fields/global variables with function pointers

Changes: https://git.openjdk.java.net/panama-foreign/pull/422/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=422&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258405
  Stats: 102 lines in 3 files changed: 87 ins; 12 del; 3 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/422.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/422/head:pull/422

PR: https://git.openjdk.java.net/panama-foreign/pull/422