RFR: 8325513: Export method for Cipher [v5]

[Weijun Wang]

> Add `Cipher::exportKey` API.

Weijun Wang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 16 additional commits since the last revision:

 - Merge branch 'master' into 8325513
 - exportData
 - plural
 - Merge branch 'master' into 8325513
 - small update
 - Merge branch 'master' into 8325513
 - change new method to non final
 - rename
 - Merge branch 'master' into 8325513
 - make test work
 - ... and 6 more: https://git.openjdk.org/jdk/compare/cdaab9e7...cd02570c

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/18409/files
  - new: https://git.openjdk.org/jdk/pull/18409/files/11701dce..cd02570c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18409&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18409&range=03-04

  Stats: 333499 lines in 3636 files changed: 87119 ins; 232474 del; 13906 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