RFR: 8365024: G1: Make G1CollectionSet::_inc_build_state assert-only [v3]

[Thomas Schatzl]

> Hi all,
> 
>   please review this change that makes the `G1CollectionSet::_inc_build_state` member debug/assert-only - it's only ever used in assertions.
> 
> Testing: local compilation, gha
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:

 - Merge branch 'master' into 8365024-inc-cset-state-assert-only
 - 8365024
   
   Hi all,
   
     please review this change that makes the `G1CollectionSet::_inc_build_state` member debug/assert-only - it's only ever used in assertions.
   
   Testing: local compilation, gha
   
   Thanks,
     Thomas
 - 8364934
   
   Hi all,
   
     please review this renaming of various members of `G1CollectionSet` to
   
   - use the same prefixes
   - remove unnecessary prefixes (`collection_set`)
   - fix some documentation
   
   Testing: gha
   
   Thanks,
     THoams
 - * remove accidentally merged in JDK-8364934
 - 8364925
   
   Hi all,
   
     please review this change that improves the G1CollectionSet incremental state handling slightly:
   
   * remove `_selected_groups_cur_length` with getter as we do not need a copy of that value around
   * move implementations of some methods from header files into cpp file
   * moved some incremental state updates from `finalize_old_part` to the respective `start/continue/stop_incremental_building` method
   
   Testing: gha
   
   Thanks,
     Thomas

-------------

Changes: https://git.openjdk.org/jdk/pull/26671/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26671&range=02
  Stats: 5 lines in 2 files changed: 2 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/26671.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26671/head:pull/26671

PR: https://git.openjdk.org/jdk/pull/26671