RFR: 8274069: Clean up g1ParScanThreadState a bit [v4]

[Thomas Schatzl]

> Hi all,
> 
>   can I have reviews for this change that does some minor refactoring for issues found in JDK-8271880/PR#5037:
> 
> - remove declaration without definition
> - move inlined code in the .hpp file into .inline.hpp file
> - factor out some code
> 
> Testing: gha, local compilation, local gc/g1
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:

  kbarrett review; fix comment, includes

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5607/files
  - new: https://git.openjdk.java.net/jdk/pull/5607/files/769254c8..5d3a28bd

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5607&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5607&range=02-03

  Stats: 31 lines in 4 files changed: 15 ins; 11 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5607.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5607/head:pull/5607

PR: https://git.openjdk.java.net/jdk/pull/5607