Port Scala.js j.u.Objects parameter widening & later changes.

[LeeTibbert]

• This PR was motivated by my attempts to use an automated
  script to port Scala.js j.u.Map. Scala.js appears to
  pay considerable attention to using Objects.equals().
  Before this PR, The Scala Native compiler would fail
  because it was looking to apply implicit conversions
  and found two, in Predef.

  After this PR, the freshly ported j.u.Map code compiles
  and executes its extensive test code without introducing
  failures elsewhere in the ensemble.

  This PR should ease future porting either way.

• This PR is pretty much an automated, but curated, port of the
  Scala.js code. As per past guidance, the Scals.js license is
  stripped. A Scala Native header is prepended, with information
  allowing future developers to synchronize this port with
  Scala.js original. The new header multi-line comment style follows
  the Scala.js original.

  The new ObjectsTests.scala contains some scalafmt differences from
  the Scala.js original. Once content has been substantially aligned
  between the two projects, perhaps there is an opportunity to reduce
  porting & review loads by aligning the automated formatting tools and/or
  rules.

• Previously, there was no j.u.Objects{Test | Suite}.
  ObjectsTests.scala was ported via script.

Documentation:

• The standard changelog entry is requested.

Testing:

Safety -

• Built and tested ("test-all") in debug mode using sbt 1.3.13 on
  X86_64 only. All tests pass.

Efficacy -

• An automated port of a private j.u.Map.scala now compiles & passes
  unit-tests without having to manually edit the file for Objects.equals().