Java: add Diagnostic Match for synthetic annotation generated by javac

Author: IdrissRio

java/ql/test/library-tests/module-import-declarations/Test.java

@@ -3,4 +3,9 @@
 class Test {
     public static void main(String[] args) {
     }
-}
+}
+
+// Diagnostic Matches: Unknown location for jdk.internal.RequiresIdentity+Annotation
+// This diagnostic shouldn't occur: jdk.internal is not exported by default,
+// but our compiler explicitly exports it via module-info.java at
+// /Users/idrissrio/github/work/semmle-code/extractor-jdk/java.base/src/module-info.java