RFR: 8297878: KEM: Implementation [v3]

[Weijun Wang]

> The KEM API and DHKEM impl. Note that this PR uses new methods in https://github.com/openjdk/jdk/pull/13250.

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

  spec changes

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13256/files
  - new: https://git.openjdk.org/jdk/pull/13256/files/8a227daf..b398b03e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13256&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13256&range=01-02

  Stats: 169 lines in 4 files changed: 106 ins; 19 del; 44 mod
  Patch: https://git.openjdk.org/jdk/pull/13256.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13256/head:pull/13256

PR: https://git.openjdk.org/jdk/pull/13256