RFR: 8357828: Add a timestamp to jcmd diagnostic commands

[Ivan Bereziuk]

`jcmd` provides great diagnostics but many commands lack a timestamp in their output.
Adding a timestamp to the output of some would add value for those debugging JVM data.

Some diagnostic commands already provide timestamps. For example `Thread.print` already prints timestamp in a "yyyy-MM-dd HH:mm:ss" format.

Adding timestamps to all diagnostic `jcmd` commands with a non-throw-away STDOUT.

The exceptions are:
* `VM.uptime` - command run with `-date` argument will also print a timestamp;
* `VM.system_properties` - already lists timestamp
* `Thread.dump_to_file` - the content dumped to file already has a timestamp;
* `VM.version`

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Commit messages:
 - copyright change
 - Thread.dump_to_file doesn't need timestamp in STDOUT
 - CodeCacheTest.java and ClassHierarchyTest.java to account for added timestamp
 - jcmd [PID] Compiler.perfmap has no valuable stdout. Remove timestamp from Compiler.perfmap
 - 8357828: add timestamps to jcmd diagnostic commands

Changes: https://git.openjdk.org/jdk/pull/27368/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27368&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357828
  Stats: 45 lines in 4 files changed: 38 ins; 3 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/27368.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27368/head:pull/27368

PR: https://git.openjdk.org/jdk/pull/27368