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

js/js.serializer/src/org/jetbrains/kotlin/serialization/js/KotlinJavascriptSerializationUtil.kt

@@ -93,7 +93,7 @@ object KotlinJavascriptSerializationUtil {
         val skip: (DeclarationDescriptor) -> Boolean = { DescriptorUtils.getContainingModule(it) != module || (it is MemberDescriptor && it.isHeader) }
 
         val fileRegistry = KotlinFileRegistry()
-        val serializerExtension = KotlinJavascriptSerializerExtension(fileRegistry, fqName)
+        val serializerExtension = KotlinJavascriptSerializerExtension(fileRegistry)
         val serializer = DescriptorSerializer.createTopLevel(serializerExtension)
 
         val classDescriptors = DescriptorSerializer.sort(
@@ -123,7 +123,7 @@ object KotlinJavascriptSerializationUtil {
         val members = fragments
                 .flatMap { fragment -> DescriptorUtils.getAllDescriptors(fragment.getMemberScope()) }
                 .filterNot(skip)
-        builder.`package` = serializer.packagePartProto(members).build()
+        builder.`package` = serializer.packagePartProto(fqName, members).build()
 
         builder.setExtension(
                 JsProtoBuf.packageFragmentFiles,

js/js.serializer/src/org/jetbrains/kotlin/serialization/js/KotlinJavascriptSerializerExtension.kt

@@ -29,9 +29,8 @@ import org.jetbrains.kotlin.serialization.SerializerExtensionProtocol
 import org.jetbrains.kotlin.types.FlexibleType
 
 class KotlinJavascriptSerializerExtension(
-        private val fileRegistry: KotlinFileRegistry,
-        packageFqName: FqName
-) : KotlinSerializerExtensionBase(JsSerializerProtocol, packageFqName) {
+        private val fileRegistry: KotlinFileRegistry
+) : KotlinSerializerExtensionBase(JsSerializerProtocol) {
     override val stringTable = JavaScriptStringTable()
 
     override fun serializeFlexibleType(flexibleType: FlexibleType, lowerProto: ProtoBuf.Type.Builder, upperProto: ProtoBuf.Type.Builder) {