RFR: 8310813: Simplify and modernize equals, hashCode, and compareTo for BigInteger [v7]

[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 14 additional commits since the last revision:

 - Merge branch 'master' into 8310813
 - Fix bugs in Shared.createSingle
 - Merge branch 'master' into 8310813
 - Group params coarser (suggested by @cl4es)
   
   - Splits 20 params into 3 groups: (S)mall, (M)edium and (L)arge.
     Every testXYZ method invokes M operations, where M is the maximum
     number of elements in a group. Shorter groups are cyclically padded.
   - Uses the org.openjdk.jmh.infra.Blackhole API and increases
     benchmark time.
   - Fixes a bug in Shared that precluded 0 from being in a pair.
 - Use better overloads (suggested by @cl4es)
   
   - Uses simpler, more suitable overloads for the subrange
     starting from 0
 - Improve benchmarks
 - Merge branch 'master' into 8310813
 - 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
 - ... and 4 more: https://git.openjdk.org/jdk/compare/1c86621d...77bfab34

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14630/files
  - new: https://git.openjdk.org/jdk/pull/14630/files/6fa3f694..77bfab34

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14630&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14630&range=05-06

  Stats: 105957 lines in 3261 files changed: 46415 ins; 17757 del; 41785 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