KT-20880: Fix AddDocumentationFix to add multiline comment

#KT-20880 fixed

idea/testData/quickfix/kdocMissingDocumentation/withIndentation.kt

@@ -0,0 +1,9 @@
+// "Add documentation" "true"
+
+
+class C {
+
+    fun <caret>foo() {
+
+    }
+}