RFR: 8377223: Port fdlibm atanh to Java [v3]

[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 one additional commit since the last revision:

  8377223: Addressed reviewer's comments.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29782/files
  - new: https://git.openjdk.org/jdk/pull/29782/files/6fea8fad..0d480b96

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29782&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29782&range=01-02

  Stats: 7 lines in 4 files changed: 2 ins; 0 del; 5 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