[foreign-jextract] RFR: 8258388: jextract should avoid $ in class name used with inheritance

[Athijegannathan Sundararajan]

all tests, samples pass 'as is'

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Commit messages:
 - 8258388: jextract should avoid $ in class name used with inheritance

Changes: https://git.openjdk.java.net/panama-foreign/pull/421/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=421&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258388
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/421.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/421/head:pull/421

PR: https://git.openjdk.java.net/panama-foreign/pull/421