[crac] RFR: CRaC related documentation in JDK classes using custom tag

[Radim Vansa]

As proposed in https://mail.openjdk.org/pipermail/crac-dev/2023-February/000496.html I am adding some CRaC related documentation.

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Commit messages:
 - CRaC related documentation in JDK classes using custom tag

Changes: https://git.openjdk.org/crac/pull/51/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=51&range=00
  Stats: 100 lines in 10 files changed: 99 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/crac/pull/51.diff
  Fetch: git fetch https://git.openjdk.org/crac pull/51/head:pull/51

PR: https://git.openjdk.org/crac/pull/51