[foreign-jextract] RFR: 8252634: jextract should generate type annotations for C types

[Athijegannathan Sundararajan]

@C annotation generated for C types

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Commit messages:
 - 8252634: jextract should generate type annotations for C types

Changes: https://git.openjdk.java.net/panama-foreign/pull/300/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=300&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252634
  Stats: 361 lines in 8 files changed: 303 ins; 0 del; 58 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/300.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/300/head:pull/300

PR: https://git.openjdk.java.net/panama-foreign/pull/300