RFR: 8354428: [ubsan] g1BiasedArray.hpp: pointer overflow in address calculation

[Thomas Schatzl]

Hi all,

  please review this fix for an ubsan error related to pointer under- or overflows when using the biased array helper.

The fix is, instead of using direct address calculations that can cause these errors, use `uintptr_t` where the overflow behavior is defined in C++. Only convert to pointer at the actual access.

Testing: gha, tier1

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Commit messages:
 - * fix copyright
 - 8354428

Changes: https://git.openjdk.org/jdk/pull/25447/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25447&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8354428
  Stats: 16 lines in 4 files changed: 0 ins; 5 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/25447.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25447/head:pull/25447

PR: https://git.openjdk.org/jdk/pull/25447