Introduce InlineClasses language feature

Allow to write `inline` modifier in front of class declaration

compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt

@@ -1,17 +1,6 @@
 /*
- * Copyright 2010-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlin.config
@@ -76,6 +65,7 @@ enum class LanguageFeature(
     ProperForInArrayLoopRangeVariableAssignmentSemantic(KOTLIN_1_3),
     NestedClassesInAnnotations(KOTLIN_1_3),
     JvmStaticInInterface(KOTLIN_1_3),
+    InlineClasses(KOTLIN_1_3),
 
     StrictJavaNullabilityAssertions(sinceVersion = null, defaultState = State.DISABLED),