RFR: 8324553: Shenandoah: Move periodic tasks closer to their collaborators [v2]

[William Kemper]

> This is a refactoring to move Shenandoah's periodic tasks from the control thread to their respective dependencies: the pacer and monitoring support. This change will facilitate reviews of the upcoming changes to isolate the generational mode changes.

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

  Improve names and conformance to style guide

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Changes:
  - all: https://git.openjdk.org/jdk/pull/17540/files
  - new: https://git.openjdk.org/jdk/pull/17540/files/635633bb..09eeaa4c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17540&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17540&range=00-01

  Stats: 27 lines in 5 files changed: 2 ins; 3 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/17540.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17540/head:pull/17540

PR: https://git.openjdk.org/jdk/pull/17540