RFR: 8366478: BigDecimal roots [v6]

[fabioromano1]

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

fabioromano1 has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains eight commits:

 - Merge branch 'openjdk:master' into 8366478
 - Restore actual BigDecimal.java
 - Update BigDecimal.java
 - Comment for error analysis
 - Code simplification
 - Code simplification
 - Removed trailing whitespaces
 - Add BigDecimal.nthRoot()

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Changes: https://git.openjdk.org/jdk/pull/27148/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27148&range=05
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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