[K/JS] Add support of compilation with ES-classes

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JSCompilerArguments.kt

@@ -291,6 +291,17 @@ class K2JSCompilerArguments : CommonCompilerArguments() {
     )
     var strictImplicitExportType: Boolean by FreezableVar(false)
 
+    @GradleOption(
+        value = DefaultValue.BOOLEAN_FALSE_DEFAULT,
+        gradleInputType = GradleInputTypes.INPUT,
+        shouldGenerateDeprecatedKotlinOptions = true,
+    )
+    @Argument(
+        value = "-Xes-classes",
+        description = "Generated JavaScript will use ES2015 classes."
+    )
+    var useEsClasses: Boolean by FreezableVar(false)
+
     @GradleOption(
         value = DefaultValue.BOOLEAN_TRUE_DEFAULT,
         gradleInputType = GradleInputTypes.INPUT,

compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/K2JsIrCompiler.kt

@@ -144,7 +144,8 @@ class K2JsIrCompiler : CLICompiler<K2JSCompilerArguments>() {
                     arguments.irSafeExternalBooleanDiagnostic,
                     messageCollector
                 ),
-                granularity = arguments.granularity
+                granularity = arguments.granularity,
+                es6mode = arguments.useEsClasses
             )
         }
 
@@ -668,7 +669,14 @@ class K2JsIrCompiler : CLICompiler<K2JSCompilerArguments>() {
                 compilerConfiguration = configurationJs,
                 irFactory = { IrFactoryImplForJsIC(WholeWorldStageController()) },
                 mainArguments = mainCallArguments,
-                compilerInterfaceFactory = { mainModule, cfg -> JsIrCompilerWithIC(mainModule, cfg, arguments.granularity) }
+                compilerInterfaceFactory = { mainModule, cfg ->
+                    JsIrCompilerWithIC(
+                        mainModule,
+                        cfg,
+                        arguments.granularity,
+                        es6mode = arguments.useEsClasses
+                    )
+                }
             )
 
             val artifacts = cacheUpdater.actualizeCaches()