RFR: 8358957: [ubsan]: The assert in layout_helper_boolean_diffbit() in klass.hpp needs UB to fail [v2]

[Afshin Zafari]

> Avoid using loop and UB in left-shift operation as suggested by Kim's comment in the JBS-issue.
> 
> Tests:
>  mach5 tiers 1-5 {macosx-aarch64, linux-x64, windows-x64} x {debug, product}

Afshin Zafari has updated the pull request incrementally with two additional commits since the last revision:

 - better
 - added post-cond and improved comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27288/files
  - new: https://git.openjdk.org/jdk/pull/27288/files/b2235d8b..165a563d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27288&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27288&range=00-01

  Stats: 3 lines in 1 file changed: 1 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27288.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27288/head:pull/27288

PR: https://git.openjdk.org/jdk/pull/27288