Support companion object factory method

Sometimes you want to perform some validation before constructing an object. A good place for that is the method factory on the companion object:

class ParamsNeedValidation private(param1: Param1, param2: Param2)
object ParamsNeedValidation {
  def apply(param1: Param1, param2: Param2) : ParamsNeedValidation = {
     // validate param1 & param2
     new ParamsNeedValidation(param1, param2)
  }
}

When the primary constructor is found to be private, macwire could give the companion object a chance and IF it has a single apply method, try it.
So we would end up with this:

lazy val pnv = wire[ParamsNeedValidation]

Turned into

lazy val pnv = ParamsNeedValidation(param1, param2)

If the companion object has more than one apply method, a compilation error is returned:

ParamsNeedValidation constructor is private and its companion object has more than one apply method:
- apply(param1, param2)
- apply(param3)

If the companion object has no apply method, then we would fail with the usual:

ParamsNeedValidation constructor is private