Added support for type attribute when parsing dependencies (#2994)

This ensures, that we can populate the `type` attribute to be used by
coursier. I have not checked whether this is self-complete to work with other
dependency type. Maybe, we need some follow up PRs to refine it.

Pull request: #2994

scalalib/src/mill/scalalib/Dep.scala

@@ -109,6 +109,7 @@ object Dep {
     val attributes = parts.tail.foldLeft(coursier.Attributes()) { (as, s) =>
       s.split('=') match {
         case Array("classifier", v) => as.withClassifier(coursier.Classifier(v))
+        case Array("type", v) => as.withType(coursier.Type(v))
         case Array(k, v) => throw new Exception(s"Unrecognized attribute: [$s]")
         case _ => throw new Exception(s"Unable to parse attribute specifier: [$s]")
       }