RFR: 8367759: G1: Move G1UpdateRegionLivenessAndSelectForRebuildTask into its own file

[Thomas Schatzl]

Hi all,

  please review this change to move `G1UpdateRegionLivenessAndSelectForRebuildTask` into a separate file. I would like to merge this class and G1BuildCandidateRegionsTask in the near future because the latter mostly repeats the work of the former anyway, but together (with helper classes) they are quite large (if not large already by themselves). This should help make `g1ConcurrentMark.cpp` a little more manageable.

There is no change in the code, just moving and fixing includes/adding forwards.

Testing: local compilation, gha

Thanks,
  Thomas

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Commit messages:
 - Update src/hotspot/share/gc/g1/g1ConcurrentMark.hpp
 - * fix compilation
 - Merge branch 'master' into 8367759-move-remark-task
 - * remove some later change
 - 8367759

Changes: https://git.openjdk.org/jdk/pull/27314/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27314&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367759
  Stats: 427 lines in 3 files changed: 254 ins; 173 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27314.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27314/head:pull/27314

PR: https://git.openjdk.org/jdk/pull/27314