RFR: JDK-8301205: Port fdlibm log10 to Java [v3]

[Joe Darcy]

> Restarting the port of FDLIBM to Java with the log10 method.
> 
> There are two port, the first a near-transliteration from C port to use as a test reference in
> 
> test/jdk/java/lang/StrictMath/FdlibmTranslit.java
> 
> and a more idiomatic Java port in 
> 
> src/java.base/share/classes/java/lang/FdLibm.java
> 
> First I debug the FdlibmTranslit port by running it against the C version. Once that is working, I copy the port into the java.lang.FdLibm.java and do a series of transformation to get the code closer to usual JDK style.

Joe Darcy has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - Merge branch 'master' into JDK-8301205
 - Add comment.
 - Reformat code some more.
 - Change to hex fp literals, misc updates.
 - Use more idiomatic style in ported FDLBIM code.
 - Merge branch 'master' into JDK-8301205
 - JDK-8301205: Port fdlibm log10 to Java

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12242/files
  - new: https://git.openjdk.org/jdk/pull/12242/files/0f74dd5f..9ae3bf20

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12242&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12242&range=01-02

  Stats: 7048 lines in 320 files changed: 1291 ins; 249 del; 5508 mod
  Patch: https://git.openjdk.org/jdk/pull/12242.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12242/head:pull/12242

PR: https://git.openjdk.org/jdk/pull/12242