This PR adds missing `@Since` and `@PreviewFeature` annotations to some of the Panama FFM entities.
This PR should also be back-ported to 21. ------------- Commit messages: - Add @Since and @PreviewFeature where missing Changes: https://git.openjdk.org/jdk/pull/14611/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14611&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8310591 Stats: 8 lines in 3 files changed: 8 ins; 0 del; 0 mod Patch: https://git.openjdk.org/jdk/pull/14611.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/14611/head:pull/14611 PR: https://git.openjdk.org/jdk/pull/14611
