Disambiguate Constructor and Method when calling getRoot().

Avoid merging Target_java_lang_reflect_Method and Target_java_lang_reflect_Constructor when calling asExecutable() by adding a separate asExecutable() method for the two.

substratevm/src/com.oracle.svm.reflect/src/com/oracle/svm/reflect/target/ReflectionHelper.java

@@ -80,7 +80,15 @@ private static Target_java_lang_reflect_Constructor asConstructor(Object object)
         return KnownIntrinsics.unsafeCast(object, Target_java_lang_reflect_Constructor.class);
     }
 
-    private static Target_java_lang_reflect_Executable asExecutable(Object object) {
+    private static Target_java_lang_reflect_Executable asExecutable(Target_java_lang_reflect_Method object) {
+        return KnownIntrinsics.unsafeCast(object, Target_java_lang_reflect_Executable.class);
+    }
+
+    private static Target_java_lang_reflect_Executable asExecutable(Target_java_lang_reflect_Constructor object) {
+        return KnownIntrinsics.unsafeCast(object, Target_java_lang_reflect_Executable.class);
+    }
+
+    private static Target_java_lang_reflect_Executable asExecutable(Target_java_lang_reflect_AccessibleObject object) {
         return KnownIntrinsics.unsafeCast(object, Target_java_lang_reflect_Executable.class);
     }