Add ProjectOpenProcessor for *.gradle.kts file to open it as project

#KT-19024 Fixed

idea/idea-gradle/idea-gradle.iml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+    <orderEntry type="library" name="gradle-and-groovy-plugin" level="project" />
+    <orderEntry type="library" name="intellij-core" level="project" />
+    <orderEntry type="library" name="kotlin-runtime" level="project" />
+    <orderEntry type="library" name="idea-full" level="project" />
+  </component>
+</module>

idea/idea-gradle/src/org/jetbrains/kotlin/gradle/GradleKotlinDSLProjectOpenProcessor.kt

@@ -0,0 +1,33 @@
+/*
+ * 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.
+ */
+
+package org.jetbrains.kotlin.gradle
+
+import com.intellij.openapi.vfs.VirtualFile
+import org.jetbrains.plugins.gradle.service.project.wizard.GradleProjectImportBuilder
+import org.jetbrains.plugins.gradle.service.project.wizard.GradleProjectOpenProcessor
+import org.jetbrains.plugins.gradle.util.GradleConstants
+
+class GradleKotlinDSLProjectOpenProcessor(builder: GradleProjectImportBuilder) : GradleProjectOpenProcessor(builder) {
+    override fun canOpenProject(file: VirtualFile): Boolean = when {
+        !file.isDirectory -> file.name.endsWith(".gradle.kts")
+        supportedExtensions.any { file.findChild(it) != null } -> true
+        else -> super.canOpenProject(file)
+    }
+
+    override fun getSupportedExtensions(): Array<String> =
+            arrayOf("${GradleConstants.DEFAULT_SCRIPT_NAME}.kts", GradleConstants.SETTINGS_FILE_NAME)
+}

idea/src/META-INF/plugin.xml

@@ -2477,6 +2477,7 @@
     <indexedRootsProvider implementation="org.jetbrains.kotlin.idea.core.script.dependencies.KotlinScriptDependenciesIndexableSetContributor"/>
     <psi.clsCustomNavigationPolicy implementation="org.jetbrains.kotlin.idea.core.script.dependencies.ScriptDependencySourceNavigationPolicyForJavaClasses"/>
     <resolveScopeProvider implementation="org.jetbrains.kotlin.idea.core.script.dependencies.KotlinScriptResolveScopeProvider"/>
+    <projectOpenProcessor implementation="org.jetbrains.kotlin.gradle.GradleKotlinDSLProjectOpenProcessor"/>
 
   </extensions>