RFR: 8367603: Optimize exact division in BigDecimal [v6]

[fabioromano1]

> A formula to lower the overestimate for the precision of an exact quotient, without introducing too expensive operations of division on numerator and denominator.
> [Here is a proof for the formula.](https://github.com/user-attachments/files/22314648/frazioni_decimali.pdf)

fabioromano1 has updated the pull request incrementally with one additional commit since the last revision:

  Extend log5Upper() for negative integers

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27271/files
  - new: https://git.openjdk.org/jdk/pull/27271/files/b3e985c2..7db21481

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27271&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27271&range=04-05

  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/27271.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27271/head:pull/27271

PR: https://git.openjdk.org/jdk/pull/27271