RFR: 8342444: Shenandoah: Uncommit regions from a separate, STS aware thread [v8]

[William Kemper]

> Currently, Shenandoah uncommits regions from its control thread. The control thread is responsible for starting GC cycles in a timely fashion. Uncommitting memory from this thread may introduce unwanted delays in the control thread's response to GC pressure.

William Kemper has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 18 additional commits since the last revision:

 - Log uncommitted delta and capacity
 - Merge remote-tracking branch 'jdk/master' into shen-uncommit-thread
 - Restore logging format, show change in committed heap, rather than usage
 - Allow commits initially
 - Use idiomatic name for CADR class
 - Improve comments
 - Do not notify uncommit thread when uncommit is forbidden
 - Prevent uncommit thread from running during GC
 - Style and formatting fixes
 - Alphabetize includes in shenandoahHeap.cpp
 - ... and 8 more: https://git.openjdk.org/jdk/compare/f2fab487...847a2593

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Changes:
  - all: https://git.openjdk.org/jdk/pull/22019/files
  - new: https://git.openjdk.org/jdk/pull/22019/files/2cb71140..847a2593

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22019&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22019&range=06-07

  Stats: 225409 lines in 4393 files changed: 87200 ins; 121188 del; 17021 mod
  Patch: https://git.openjdk.org/jdk/pull/22019.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22019/head:pull/22019

PR: https://git.openjdk.org/jdk/pull/22019