detect Kotlin source roots

#KT-8592 Fixed

idea/src/META-INF/plugin.xml

@@ -530,6 +530,8 @@
     <library.presentationProvider implementation="org.jetbrains.kotlin.idea.framework.JavaRuntimePresentationProvider"/>
     <library.presentationProvider implementation="org.jetbrains.kotlin.idea.framework.JSLibraryStdPresentationProvider"/>
 
+    <library.javaSourceRootDetector implementation="org.jetbrains.kotlin.idea.configuration.KotlinSourceRootDetector"/>
+
     <typeHierarchyProvider language="kotlin" implementationClass="org.jetbrains.kotlin.idea.hierarchy.KotlinTypeHierarchyProvider"/>
     <callHierarchyProvider
         language="kotlin"

idea/src/org/jetbrains/kotlin/idea/configuration/KotlinSourceRootDetector.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2010-2016 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.
+ */
+
+package org.jetbrains.kotlin.idea.configuration
+
+import com.intellij.openapi.roots.OrderRootType
+import com.intellij.openapi.roots.libraries.ui.FileTypeBasedRootFilter
+import org.jetbrains.kotlin.idea.KotlinFileType
+
+class KotlinSourceRootDetector : FileTypeBasedRootFilter(OrderRootType.SOURCES, false, KotlinFileType.INSTANCE, "sources")