RFR: 8370628: Rename BigInteger::nthRoot to rootn, and similarly for nthRootAndRemainder [v2]

[Raffaello Giulietti]

> The reason for this last minute renaming is to more closely adhere to the IEEE 754 nomenclature, even in the BigInteger class (and in the internal MutableBigInteger).

Raffaello Giulietti has updated the pull request incrementally with one additional commit since the last revision:

  Rename invocations in tests.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27980/files
  - new: https://git.openjdk.org/jdk/pull/27980/files/801e4440..ed9ff931

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27980&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27980&range=00-01

  Stats: 44 lines in 1 file changed: 0 ins; 0 del; 44 mod
  Patch: https://git.openjdk.org/jdk/pull/27980.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27980/head:pull/27980

PR: https://git.openjdk.org/jdk/pull/27980