[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)
         }
     }
 

js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/JsBlock.java

@@ -8,7 +8,6 @@ import org.jetbrains.kotlin.js.util.AstUtil;
 import org.jetbrains.annotations.NotNull;
 import com.intellij.util.SmartList;
 
-import java.util.ArrayList;
 import java.util.List;
 
 /**
@@ -19,7 +18,7 @@ public class JsBlock extends SourceInfoAwareJsNode implements JsStatement {
     private final List<JsStatement> statements;
 
     public JsBlock() {
-        this(new ArrayList<JsStatement>());
+        this(new SmartList<JsStatement>());
     }
 
     public JsBlock(JsStatement statement) {

js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/JsCompositeBlock.kt

@@ -9,7 +9,11 @@ import org.jetbrains.kotlin.js.util.AstUtil;
 /**
  * Represents a JavaScript block which could not be rendered into a material one.
  */
-class JsCompositeBlock(statements: List<JsStatement> = mutableListOf()) : JsBlock(statements) {
+class JsCompositeBlock : JsBlock {
+    constructor() : super()
+    constructor(statement: JsStatement) : super(statement)
+    constructor(statements: List<JsStatement>) : super(statements)
+
     override fun isTransparent(): Boolean {
         return true
     }
@@ -20,4 +24,4 @@ class JsCompositeBlock(statements: List<JsStatement> = mutableListOf()) : JsBloc
         globalBlockCopy.statements.addAll(statementscopy);
         return globalBlockCopy.withMetadataFrom(this);
     }
-}
+}