Fix stub generator

Add line break after all stubbed annotations to avoid malformed code

See https://github.com/github/codeql/pull/8695\#discussion_r985674245

Author: atorralba

java/ql/src/utils/stub-generator/Stubs.qll

@@ -36,12 +36,15 @@ abstract private class GeneratedType extends ClassOrInterface {
   }
 
   private string stubAnnotations() {
-    result =
-      concat(Annotation an |
-        this.(AnnotationType).getAnAnnotation() = an
-      |
-        stubAnnotation(an), "\n" order by an.getType().getQualifiedName()
-      )
+    if exists(this.(AnnotationType).getAnAnnotation())
+    then
+      result =
+        concat(Annotation an |
+            this.(AnnotationType).getAnAnnotation() = an
+          |
+            stubAnnotation(an), "\n" order by an.getType().getQualifiedName()
+          ) + "\n"
+    else result = ""
   }
 
   /** Gets the entire Java stub code for this type. */

java/ql/test/query-tests/Stubs/Minimal/MinimalStubsFromSource.expected

@@ -1,5 +1,5 @@
 noGeneratedStubs
 multipleGeneratedStubs
 #select
-| org.test.SampleAnnotationType | // Generated automatically from org.test.SampleAnnotationType for testing purposes\n\npackage org.test;\n\nimport java.lang.annotation.Annotation;\nimport java.lang.annotation.ElementType;\nimport java.lang.annotation.Target;\n\n@Target(value={java.lang.annotation.ElementType.METHOD})public @interface SampleAnnotationType\n{\n}\n |
+| org.test.SampleAnnotationType | // Generated automatically from org.test.SampleAnnotationType for testing purposes\n\npackage org.test;\n\nimport java.lang.annotation.Annotation;\nimport java.lang.annotation.ElementType;\nimport java.lang.annotation.Target;\n\n@Target(value={java.lang.annotation.ElementType.METHOD})\npublic @interface SampleAnnotationType\n{\n}\n |
 | org.test.SampleType | // Generated automatically from org.test.SampleType for testing purposes\n\npackage org.test;\n\n\npublic class SampleType\n{\n    public Object sampleField = null;\n    public SampleType(){}\n    public void sampleMethod(){}\n}\n |