RFR: 8325513: Export method for Cipher

[Weijun Wang]

Add `Cipher::export` API.

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Commit messages:
 - Merge branch 'master' into 8325513
 - make test work
 - Add test
 - Wording
 - Wording
 - relax requirement
 - wording
 - the fix

Changes: https://git.openjdk.org/jdk/pull/18409/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18409&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325513
  Stats: 176 lines in 3 files changed: 175 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18409.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18409/head:pull/18409

PR: https://git.openjdk.org/jdk/pull/18409