SI-8072 rationalize public implicits in scala parallel collections

Pretty much everything seems like it's intended for internal use, so I moved it to a package-private object.

Split toParArray out and put it in an implicit class.  Added ability to .toParArray from Array and String also.

Added test to verify implicits are gone.
Merge pull request #3529 from Ichoran/issue/8072

SI-8072 rationalize public implicits in scala parallel collections