Move HListFormats to collection to drop cache->collection dep

Looks like the reason that util-cache depended on util-collection was to
define the sjson-new formats (HListFormats) for util-collection's HList.
Given that util-collection already depends on sjsonnew, HListFormats can
also be defined in util-collection.

All that was left then was (a) HListFormatSpec requires
sjsonnewScalaJson, so that was added in test scope, and (b) HListFormats
had to be dropped from sbt.util.CacheImplicits - HListFormats will have
to be imported and/or mixed-in where required downstream. For importing
convenience I defined a companion object.

build.sbt

@@ -83,7 +83,7 @@ lazy val utilCollection = (project in internalPath / "util-collection").
     crossScalaVersions := Seq(scala210, scala211, scala212),
     Util.keywordsSettings,
     name := "Util Collection",
-    libraryDependencies ++= Seq(sjsonnew.value)
+    libraryDependencies ++= Seq(sjsonnew.value, sjsonnewScalaJson.value % Test)
   )
 
 lazy val utilApplyMacro = (project in internalPath / "util-appmacro").
@@ -140,7 +140,7 @@ lazy val utilLogic = (project in internalPath / "util-logic").
 
 // Persisted caching based on sjson-new
 lazy val utilCache = (project in file("util-cache")).
-  dependsOn(utilCollection, utilTesting % Test).
+  dependsOn(utilTesting % Test).
   settings(
     commonSettings,
     name := "Util Cache",

internal/util-collection/src/main/scala/sbt/internal/util/HListFormats.scala

@@ -66,3 +66,5 @@ trait HListFormats {
     def read[J](jsOpt: Option[J], unbuilder: Unbuilder[J]) = hnil
   }
 }
+
+object HListFormats extends HListFormats

internal/util-collection/src/test/scala/HListFormatSpec.scala

@@ -1,9 +1,10 @@
-package sbt.util
+package sbt
+package internal
+package util
 
 import scalajson.ast.unsafe._
-import sjsonnew._, support.scalajson.unsafe._
-import CacheImplicits._
-import sbt.internal.util.{ UnitSpec, HNil }
+import sjsonnew._, BasicJsonProtocol._, support.scalajson.unsafe._
+import HListFormats._
 
 class HListFormatSpec extends UnitSpec {
   val quux = 23 :+: "quux" :+: true :+: HNil

util-cache/src/main/scala/sbt/util/CacheImplicits.scala

@@ -1,9 +1,7 @@
 package sbt.util
 
 import sjsonnew.BasicJsonProtocol
-import sbt.internal.util.HListFormats
 
 object CacheImplicits extends CacheImplicits
 trait CacheImplicits extends BasicCacheImplicits
   with BasicJsonProtocol
-  with HListFormats