RFR: 8320112 GenShen: Improve end of process report [v2]

[William Kemper]

> When Shenandoah is shutdown, it logs a summary of its activity over the life of the process. This change adds percentages to the breakdown of the types and counts of cycles that executed. It also simplifies some of the logic around recording the various outcomes.

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

 - Reduce visibility of new methods
 - Fix accidental whitespace change

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Changes:
  - all: https://git.openjdk.org/shenandoah/pull/357/files
  - new: https://git.openjdk.org/shenandoah/pull/357/files/3ea5e980..410c731d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=357&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=357&range=00-01

  Stats: 24 lines in 4 files changed: 1 ins; 5 del; 18 mod
  Patch: https://git.openjdk.org/shenandoah/pull/357.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/357/head:pull/357

PR: https://git.openjdk.org/shenandoah/pull/357