Kotlin: Add a test for file classes

Author: igfoo

java/ql/test/library-tests/file_classes/A.kt

@@ -0,0 +1,2 @@
+fun a() {
+}

java/ql/test/library-tests/file_classes/B.kt

@@ -0,0 +1,3 @@
+fun b() {
+    a()
+}

java/ql/test/library-tests/file_classes/C.kt

@@ -0,0 +1,3 @@
+class C {
+    fun c() {}
+}

java/ql/test/library-tests/file_classes/classes.expected

@@ -0,0 +1,3 @@
+| A.kt:0:0:0:0 | AKt | true |
+| B.kt:0:0:0:0 | BKt | true |
+| C.kt:1:1:3:1 | C | false |

java/ql/test/library-tests/file_classes/classes.ql

@@ -0,0 +1,5 @@
+import java
+
+from Class c
+where c.fromSource()
+select c, any(boolean b | if c.isFileClass() then b = true else b = false)