RFR: 8366478: BigDecimal roots [v10]

[fabioromano1]

> An implementation of `BigDecimal.nthRoot(int, MathContext)`.

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

 - Correct expected scale in sqrt zero tests
 - Implement correct rounding for n < 0

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27148/files
  - new: https://git.openjdk.org/jdk/pull/27148/files/ae59e275..3d4bad30

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27148&range=09
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27148&range=08-09

  Stats: 131 lines in 2 files changed: 68 ins; 38 del; 25 mod
  Patch: https://git.openjdk.org/jdk/pull/27148.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27148/head:pull/27148

PR: https://git.openjdk.org/jdk/pull/27148