RFR: 8310813: Simplify and modernize equals, hashCode, and compareTo for BigInteger [v3]

[Pavel Rappo]

> Please review this PR to use modern APIs and language features to simplify equals, hashCode, and compareTo for BigInteger. If you have any performance concerns, please raise them.
> 
> This PR is cherry-picked from a bigger, not-yet-published PR, to test the waters. That latter PR will be published soon.

Pavel Rappo 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:

 - Restore hash code values
   
   BigInteger is old and ubiquitous enough so that there might be
   inadvertent dependencies on its hash code.
   
   This commit also includes a test, to make sure hash code is
   unchanged.
 - Merge branch 'master' into 8310813
 - Add a benchmark
 - Merge branch 'master' into 8310813
 - Use fewer range checks to improve performance
 - Improve
 - Initial commit

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14630/files
  - new: https://git.openjdk.org/jdk/pull/14630/files/9f838612..d087a592

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14630&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14630&range=01-02

  Stats: 71081 lines in 934 files changed: 19355 ins; 49233 del; 2493 mod
  Patch: https://git.openjdk.org/jdk/pull/14630.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14630/head:pull/14630

PR: https://git.openjdk.org/jdk/pull/14630