RFR: 8377223: Port fdlibm atanh to Java [v2]

[Anton Artemov]

> Hi, please consider the following changes:
> 
> This is a port of FDLIBM atanh method.

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

 - Empty commit.
 - 8377223: Addressed reviewers' comments.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/29782/files
  - new: https://git.openjdk.org/jdk/pull/29782/files/b7183e72..6fea8fad

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29782&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29782&range=00-01

  Stats: 20 lines in 2 files changed: 1 ins; 7 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/29782.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29782/head:pull/29782

PR: https://git.openjdk.org/jdk/pull/29782