RFR: 8077587: BigInteger Roots [v21]

[fabioromano1]

> This PR implements nth root computation for `BigInteger`s using Newton method and optimizes `BigInteger.pow(int)` method.
> [Here is a proof of convergence of the recurrence used.](https://github.com/user-attachments/files/19785045/nth_root_newton_proof_integers.pdf)

fabioromano1 has updated the pull request incrementally with two additional commits since the last revision:

 - Merge branch 'BigInteger-nth-root' of https://github.com/fabioromano1/jdk into BigInteger-nth-root
 - Revert format code changes

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24690/files
  - new: https://git.openjdk.org/jdk/pull/24690/files/e11b32f5..8de6b825

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24690&range=20
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24690&range=19-20

  Stats: 9 lines in 1 file changed: 0 ins; 0 del; 9 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