RFR: 8331008: Implement JEP 478: Key Derivation Function API (Preview) [v68]

[Kevin Driver]

> Introduce an API for Key Derivation Functions (KDFs), which are cryptographic algorithms for deriving additional keys from a secret key and other data. See [JEP 478](https://openjdk.org/jeps/478).

Kevin Driver has updated the pull request incrementally with two additional commits since the last revision:

 - additional clarification around KDFSpi thread safety characteristics
 - clarify that ikm and salt "getters" return the values in the order they were added

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18924/files
  - new: https://git.openjdk.org/jdk/pull/18924/files/84a0a765..997bc171

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18924&range=67
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18924&range=66-67

  Stats: 12 lines in 2 files changed: 2 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/18924.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18924/head:pull/18924

PR: https://git.openjdk.org/jdk/pull/18924