Kotlin: Add test case for variables named underscore

Author: tamasvajk

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

@@ -0,0 +1,11 @@
+fun fn() {
+    try {
+        val l = listOf(1, 2, 3)
+        l.forEachIndexed { index, _ -> println(index) }
+
+        val p = Pair(1, 2)
+        val (first, _) = p
+    } catch (_: Exception) {
+        // expected
+    }
+}

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

@@ -0,0 +1 @@
+| Test.kt:8:14:8:25 | Exception _ | Use of underscore as a one-character identifier. |

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

@@ -0,0 +1 @@
+Compatibility/JDK9/UnderscoreIdentifier.ql

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

@@ -0,0 +1,7 @@
+| Test.kt:3:9:3:31 | List<Integer> l |
+| Test.kt:4:28:4:32 | index |
+| Test.kt:4:35:4:35 | p1 |
+| Test.kt:6:9:6:26 | Pair<Integer,Integer> p |
+| Test.kt:7:14:7:18 | int first |
+| Test.kt:7:26:7:26 | Pair<Integer,Integer> tmp0_container |
+| Test.kt:8:14:8:25 | Exception _ |

java/ql/test/kotlin/query-tests/UnderscoreIdentifier/test.ql

@@ -0,0 +1,3 @@
+import java
+
+query predicate variables(Variable v) { v.fromSource() }