[JS IR] Optimize JS AST blocks memory consumption

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/codegen/IrToJs.kt

@@ -423,7 +423,7 @@ private val IrModuleFragment.jsModuleName: String
     get() = name.asString().dropWhile { it == '<' }.dropLastWhile { it == '>' }
 
 private fun List<JsStatement>.toJsCodeString(): String =
-    JsCompositeBlock().also { it.statements += this }.toString()
+    JsCompositeBlock(this).toString()
 
 enum class JsGenerationGranularity {
     WHOLE_PROGRAM,

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/JsCallTransformer.kt

@@ -31,7 +31,7 @@ class JsCallTransformer(private val jsOrJsFuncCall: IrCall, private val context:
             0 -> JsEmpty
             1 -> newStatements.single().withSource(jsOrJsFuncCall, context)
             // TODO: use transparent block (e.g. JsCompositeBlock)
-            else -> JsCompositeBlock().apply { statements += newStatements }
+            else -> JsCompositeBlock(newStatements)
         }
     }