RFR: 8367603: Optimize exact division in BigDecimal

[fabioromano1]

A formula to lower the overestimate for the precision of an exact quotient, without introduce 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)

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Commit messages:
 - Add time tests
 - Added link to proof
 - Optimize exact division

Changes: https://git.openjdk.org/jdk/pull/27271/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27271&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367603
  Stats: 199 lines in 2 files changed: 175 ins; 16 del; 8 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