RFR: 8325517: Shenandoah: Reduce unnecessary includes from shenandoahControlThread.cpp

[William Kemper]

The control thread used to run much more of the cycle directly. This code was all factored out into different classes, but many of the vestigial headers remained. Removing these improves compilation times and makes maintenance easier.

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Commit messages:
 - Oops, picked an extra cherry
 - Reduce unnecessary includes from shenandoahControlThread.cpp

Changes: https://git.openjdk.org/jdk/pull/17778/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17778&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325517
  Stats: 21 lines in 5 files changed: 9 ins; 12 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17778.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17778/head:pull/17778

PR: https://git.openjdk.org/jdk/pull/17778