[crac] RFR: 8346386: [CRaC] Move CRaC’s Java code out of restricted packages

[Timofei Pushkin]

To circumvent CRaC's limiting not-yet-standardized status:
1. Moved CRaC interface from `javax.crac` in `java.base` to `jdk.crac` in a new `jdk.crac` module.
2. Moved CRaC implementation from `jdk.crac` to `jdk.internal.crac.mirror`, both inside `java.base`. The whole CRaC implementation now resides in `jdk.internal.crac` which is exported (partially) only to the new `jdk.crac` module.

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Commit messages:
 - 8346386: [CRaC] Move CRaC’s Java code out of restricted packages

Changes: https://git.openjdk.org/crac/pull/164/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=164&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346386
  Stats: 705 lines in 62 files changed: 318 ins; 291 del; 96 mod
  Patch: https://git.openjdk.org/crac/pull/164.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/164/head:pull/164

PR: https://git.openjdk.org/crac/pull/164