RFR: 8310643: Misformatted copyright messages in FFM

[Per Minborg]

This PR suggests updating some of the ill-formed copyright headers in the FFM API and the implementation and test thereof.

Some of the test files will have now the "classpath" exception. Is this correct?

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Commit messages:
 - Update copyright formatting

Changes: https://git.openjdk.org/jdk/pull/15042/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15042&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310643
  Stats: 1083 lines in 54 files changed: 169 ins; 114 del; 800 mod
  Patch: https://git.openjdk.org/jdk/pull/15042.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15042/head:pull/15042

PR: https://git.openjdk.org/jdk/pull/15042