RFR: Add an option to stream region sampling data to a file [v2]

[William Kemper]

> This change adds two command line options to enable and configure a feature that has Shenandoah stream region sampling data to disk. These changes are complemented by changes in the [Shenandoah Visualizer](https://github.com/openjdk/shenandoah-visualizer) project to load and replay the logged region sampling data.

William Kemper has updated the pull request incrementally with two additional commits since the last revision:

 - Whitespace fixes
 - Update copyright headers

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Changes:
  - all: https://git.openjdk.java.net/shenandoah/pull/82/files
  - new: https://git.openjdk.java.net/shenandoah/pull/82/files/6cedcbc4..e93d18d7

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=82&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=82&range=00-01

  Stats: 11 lines in 4 files changed: 2 ins; 6 del; 3 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/82.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/82/head:pull/82

PR: https://git.openjdk.java.net/shenandoah/pull/82