Dedicated product for all package collections stuff

Author: yim-lee

Package.swift

@@ -40,7 +40,6 @@ let package = Package(
                 "SPMLLBuild",
                 "PackageCollections",
                 "PackageCollectionsModel",
-                "PackageCollectionsSigning",
                 "LLBuildManifest",
                 "PackageModel",
                 "PackageLoading",
@@ -58,7 +57,6 @@ let package = Package(
                 "LLBuildManifest",
                 "PackageCollections",
                 "PackageCollectionsModel",
-                "PackageCollectionsSigning",
                 "PackageModel",
                 "PackageLoading",
                 "PackageGraph",
@@ -97,6 +95,16 @@ let package = Package(
             name: "PackageCollectionsModel",
             targets: ["PackageCollectionsModel"]
         ),
+        
+        .library(
+            name: "SwiftPMPackageCollections",
+            targets: [
+                "PackageCollections",
+                "PackageCollectionsModel",
+                "PackageCollectionsSigning",
+                "PackageModel"
+            ]
+        ),
     ],
     targets: [
         // The `PackageDescription` targets define the API which is available to