[crac] RFR: API for restore time

[Anton Kozlov]

This PR adds an ability to get restore time, similar to RuntimeMXBean.getUptime() [1] and getStartTime(). Before I used to print timestamps and parse console output, which was not very convenient.

[1] https://docs.oracle.com/en/java/javase/17/docs/api/java.management/java/lang/management/RuntimeMXBean.html#getUptime()

-------------

Commit messages:
 - Cleanup
 - Highlight global variables
 - Add new pacakge description
 - Update interface
 - Fallback to the restore complete time
 - Add missing CRaCMXBean
 - Pass restore time/counter
 - Extract read_from
 - Add CRaCMXBean
 - Prepare CracRestoreParameters for extension

Changes: https://git.openjdk.org/crac/pull/29/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=29&range=00
  Stats: 561 lines in 13 files changed: 427 ins; 69 del; 65 mod
  Patch: https://git.openjdk.org/crac/pull/29.diff
  Fetch: git fetch https://git.openjdk.org/crac pull/29/head:pull/29

PR: https://git.openjdk.org/crac/pull/29