RFR: 8325513: Export method for Cipher [v7]

[Weijun Wang]

> Add `Cipher::exportKey` API.

Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:

  state check; arg check; much more test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18409/files
  - new: https://git.openjdk.org/jdk/pull/18409/files/9f9cd651..2da969c0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18409&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18409&range=05-06

  Stats: 113 lines in 3 files changed: 82 ins; 3 del; 28 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