RFR: 8377164: G1: Clean up g1BlockOffsetTable.hpp

[Thomas Schatzl]

Hi all,

  please review this cleanup of `g1BlockOffsetTable` files:

* fix includes
* move non-one-liners to hpp file
* move method implementations only referenced in cpp file to cpp file
* made some methods static

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - 8377164

Changes: https://git.openjdk.org/jdk/pull/29649/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29649&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377164
  Stats: 45 lines in 3 files changed: 20 ins; 21 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/29649.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29649/head:pull/29649

PR: https://git.openjdk.org/jdk/pull/29649