KotlinGenerateToStringAction: should generate .contentToString instead java.util.Arrays.toString

#KT-27563 Fixed

idea/testData/codeInsight/generate/toString/singleTemplate/nullableArrays.kt

@@ -0,0 +1,8 @@
+// GENERATOR: SINGLE_TEMPLATE
+class A(val n: IntArray?, val s: Array<String>) {<caret>
+    val f: Float = 1.0f
+
+    fun foo() {
+
+    }
+}