"Convert lambda to reference": fix false positive for vararg function

#KT-16422 Fixed

idea/testData/intentions/convertLambdaToReference/varargFunction.kt

@@ -0,0 +1,5 @@
+// IS_APPLICABLE: false
+// WITH_RUNTIME
+fun test(i: Int?): IntArray? {
+    return i?.let { <caret>intArrayOf(it) }
+}

idea/testData/intentions/convertLambdaToReference/varargFunction2.kt

@@ -0,0 +1,6 @@
+// WITH_RUNTIME
+fun test(vararg i: Int): IntArray {
+    return i.let { <caret>double(*it) }
+}
+
+fun double(vararg elements: Int): IntArray = elements.map { it * 2 }.toIntArray()

idea/testData/intentions/convertLambdaToReference/varargFunction2.kt.after

@@ -0,0 +1,6 @@
+// WITH_RUNTIME
+fun test(vararg i: Int): IntArray {
+    return i.let(::double)
+}
+
+fun double(vararg elements: Int): IntArray = elements.map { it * 2 }.toIntArray()