Kotlin: Add FP test cases for autoboxing query

Author: tamasvajk

java/ql/test/kotlin/query-tests/AutoBoxing/AutoBoxing.expected

@@ -0,0 +1 @@
+| Test.kt:3:17:3:17 | x | This expression is implicitly unboxed. |

java/ql/test/kotlin/query-tests/AutoBoxing/AutoBoxing.qlref

@@ -0,0 +1 @@
+Violations of Best Practice/legacy/AutoBoxing.ql

java/ql/test/kotlin/query-tests/AutoBoxing/Test.kt

@@ -0,0 +1,5 @@
+fun foo(x: Int?) {
+    if (x != null) {
+        println(x)
+    }
+}