RFR: JDK-8338587 - Internal XOF Methods for SHAKE128 and SHAKE256

[Ferenc Rakoczi]

In preparation for the new PQC algorithms implementations, internal XOF (eXtendable Output Function) methods are added to the SHAKE128 and SHAKE256 implementations.

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Commit messages:
 - Cosmetic fixes
 - JDK-8338587 - Internal XOF Methods for SHAKE128 and SHAKE256

Changes: https://git.openjdk.org/jdk/pull/20631/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20631&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338587
  Stats: 318 lines in 7 files changed: 193 ins; 99 del; 26 mod
  Patch: https://git.openjdk.org/jdk/pull/20631.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20631/head:pull/20631

PR: https://git.openjdk.org/jdk/pull/20631