[foreign-jextract] RFR: 8264825: update libclang bindings after recent jextract changes

[Athijegannathan Sundararajan]

* Fixed redundant cast generation (which leads to build warnings after libclang is regenerated)
* libclang binding regenerated and calling code adjusted.
* All tests and samples pass

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Commit messages:
 - 8264825: update libclang bindings after recent jextract changes

Changes: https://git.openjdk.java.net/panama-foreign/pull/491/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=491&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264825
  Stats: 3409 lines in 12 files changed: 1595 ins; 1032 del; 782 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/491.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/491/head:pull/491

PR: https://git.openjdk.java.net/panama-foreign/pull/491