[foreign-abi] RFR: 8247488: Add support for string helpers in CSupport

[Maurizio Cimadamore]

This fixes the javadoc mix up with charsets.

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Commit messages:
 - Fix javadoc

Changes: https://git.openjdk.java.net/panama-foreign/pull/203/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/203/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8247488
  Stats: 11 lines in 1 file changed: 0 ins; 3 del; 8 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/203.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/203/head:pull/203

PR: https://git.openjdk.java.net/panama-foreign/pull/203