RFR: 8304712: Only pass total number of regions into G1Policy::calc_min_old_cset_length

[Thomas Schatzl]

Hi all,

  please review this change that refactors `G1Policy::calc_min_old_cset_length` to take only required parameters and also just use `ceil()` for the calculation. It just does not matter to be clever here imo.

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - Just use ceil()
 - moving cast around
 - fix compilation on windows
 - Initial version

Changes: https://git.openjdk.org/jdk/pull/13147/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13147&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304712
  Stats: 16 lines in 3 files changed: 1 ins; 6 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/13147.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13147/head:pull/13147

PR: https://git.openjdk.org/jdk/pull/13147