RFR: 8305716: Enhancements for printing age tables [v2]

[William Kemper]

> In order to reduce the number of changes for the upcoming PR for the generational mode for Shenandoah we are opening separate PRs for the changes in common code. Shenandoah will be using this `AgeTable` class. There are two changes here:
> * `AgeTables` created with global=false will no longer SEGV when printing
> * A method was added to allow the `AgeTable` to print to an existing output stream

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Fix indentation

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13377/files
  - new: https://git.openjdk.org/jdk/pull/13377/files/0c1fcefa..56d59de4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13377&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13377&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13377.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13377/head:pull/13377

PR: https://git.openjdk.org/jdk/pull/13377