RFR: 7903910: JMH: Strengthen manual hierarchical padding

[Aleksey Shipilev]

Generated code uses 256 byte fields to provide hierarchical padding. JMH infrastructure classes, however, only do 128 boolean fields. We need to make sure we use the same padding code in manual infra as in the generated code.

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Commit messages:
 - Add comment
 - Fix

Changes: https://git.openjdk.org/jmh/pull/146/files
  Webrev: https://webrevs.openjdk.org/?repo=jmh&pr=146&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903910
  Stats: 560 lines in 7 files changed: 208 ins; 277 del; 75 mod
  Patch: https://git.openjdk.org/jmh/pull/146.diff
  Fetch: git fetch https://git.openjdk.org/jmh.git pull/146/head:pull/146

PR: https://git.openjdk.org/jmh/pull/146