Refactor serialization of package FQ name extension

Instead of requiring to pass it in SerializerExtensionBase's
constructor, pass it always in serializePackage. This is more
straightforward and helps in a situation where one SerializerExtension
instance is used for the whole module, not one per-package

compiler/builtins-serializer/src/org/jetbrains/kotlin/serialization/MetadataSerializer.kt

@@ -141,11 +141,11 @@ open class MetadataSerializer(private val dependOnOldBuiltIns: Boolean) {
     protected inner class PackageSerializer(
             private val classes: Collection<DeclarationDescriptor>,
             private val members: Collection<DeclarationDescriptor>,
-            packageFqName: FqName,
+            private val packageFqName: FqName,
             private val destFile: File
     ) {
         private val proto = ProtoBuf.PackageFragment.newBuilder()
-        private val extension = BuiltInsSerializerExtension(packageFqName)
+        private val extension = BuiltInsSerializerExtension()
 
         fun run() {
             serializeClasses(classes)
@@ -170,7 +170,7 @@ open class MetadataSerializer(private val dependOnOldBuiltIns: Boolean) {
         }
 
         private fun serializeMembers(members: Collection<DeclarationDescriptor>) {
-            proto.`package` = DescriptorSerializer.createTopLevel(extension).packagePartProto(members).build()
+            proto.`package` = DescriptorSerializer.createTopLevel(extension).packagePartProto(packageFqName, members).build()
         }
 
         private fun serializeStringTable() {

compiler/builtins-serializer/src/org/jetbrains/kotlin/serialization/builtins/BuiltInsSerializerExtension.kt

@@ -17,9 +17,8 @@
 package org.jetbrains.kotlin.serialization.builtins
 
 import org.jetbrains.kotlin.builtins.BuiltInSerializerProtocol
-import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.serialization.KotlinSerializerExtensionBase
 
-class BuiltInsSerializerExtension(packageFqName: FqName) : KotlinSerializerExtensionBase(BuiltInSerializerProtocol, packageFqName) {
+class BuiltInsSerializerExtension : KotlinSerializerExtensionBase(BuiltInSerializerProtocol) {
     override fun shouldUseTypeTable(): Boolean = true
 }