[JS IR] IrFactory which saves signatures for declarations created in BE

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/PersistentApi.kt

@@ -34,4 +34,8 @@ open class StageController(open val currentStage: Int = 0) {
     open fun createSignature(parentSignature: IdSignature): IdSignature? = null
 
     open val currentDeclaration: IrDeclaration? get() = null
+}
+
+interface IdSignatureRetriever {
+    fun declarationSignature(declaration: IrDeclaration): IdSignature?
 }