RFR: 8318096: Add getParams method in PublicKey and PrivateKey

[Weijun Wang]

Add `getParams` to `PublicKey` and `PrivateKey` so it's available to all current and future public and private keys.

No test. Might add one.

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Commit messages:
 - 8318096: Add getParams method in PublicKey and PrivateKey

Changes: https://git.openjdk.org/jdk/pull/16222/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16222&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318096
  Stats: 256 lines in 16 files changed: 238 ins; 0 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/16222.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16222/head:pull/16222

PR: https://git.openjdk.org/jdk/pull/16222