RFR: 8324981: Shenandoah: Move commit and soft max heap changed methods into heap

[William Kemper]

These methods could have been static in control thread because they only interact with the heap. Moving them into the heap reduces code duplication on the generational mode branch.

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Commit messages:
 - Move uncommit methods from control thread to heap

Changes: https://git.openjdk.org/jdk/pull/17634/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17634&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324981
  Stats: 109 lines in 4 files changed: 53 ins; 53 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/17634.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17634/head:pull/17634

PR: https://git.openjdk.org/jdk/pull/17634