RFR: 8319174: Enhance robustness of some j.m.BigInteger constructors [v5]

[Raffaello Giulietti]

> Enhance `java.math.BigInteger` constructors taking a `byte[]` argument by improving guarantees of internal invariants.

Raffaello Giulietti has updated the pull request incrementally with one additional commit since the last revision:

  Changed behavior on len == 0.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16449/files
  - new: https://git.openjdk.org/jdk/pull/16449/files/eafa99c1..57043db1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16449&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16449&range=03-04

  Stats: 8 lines in 1 file changed: 5 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16449.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16449/head:pull/16449

PR: https://git.openjdk.org/jdk/pull/16449