RFR: 8377223: Port fdlibm atanh to Java [v5]

[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: Added case |x| > to docs.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/29782/files
  - new: https://git.openjdk.org/jdk/pull/29782/files/e3cfea68..815ce7d8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29782&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29782&range=03-04

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