RFR: 8077587: BigInteger Roots

[fabioromano1]

This PR implements nth root computation for `BigInteger`s using Newton method and optimizes `BigInteger.pow(int)` method.

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Commit messages:
 - Remove trailing whitespaces
 - Merge branch 'openjdk:master' into BigInteger-nth-root
 - Add nthRoot(int) methods and optimize pow(int)

Changes: https://git.openjdk.org/jdk/pull/24690/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24690&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8077587
  Stats: 246 lines in 2 files changed: 207 ins; 16 del; 23 mod
  Patch: https://git.openjdk.org/jdk/pull/24690.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24690/head:pull/24690

PR: https://git.openjdk.org/jdk/pull/24690