Kapt: support multiple annotation processing steps (KT-13651)

(cherry picked from commit 880e183)

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

@@ -0,0 +1,22 @@
+/*
+ * 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.config
+
+import com.intellij.openapi.util.Key
+import java.io.File
+
+val APPEND_JAVA_SOURCE_ROOTS_HANDLER_KEY = Key<(List<File>) -> Unit>("AppendJavaSourceRootsHandlerKey")