error.c: Update the message format for NoMethodError

* If the receiver is a Class, use "... for class <class name>".
* If the receiver is a Module, use "... for module <module name>".
* If the receiver is an extended object (i.e., has a singleton class),
  use "... for <rb_any_to_s(receiver)>".
* Otherwise, use "... for an instance of <class name>".

Examples:

```
42.time    #=> undefined method `time' for an instance of Integer (NoMethodError)

class Foo
  privatee #=> undefined local variable or method 'privatee' for class Foo (NoMethodError)
end

def (o=Object.new).foo
end
o.bar      #=> undefined method `bar' for #<Object: 0xdeadbeef(any_to_s)> (NoMethodError)
```

1 files changed, 5 insertions, 3 deletions

diff --git a/error.c b/error.c
index affee7d828..727697542f 100644
--- a/error.c
+++ b/error.c
@@ -2116,12 +2116,14 @@ name_err_mesg_to_str(VALUE obj)
 object:
                 klass = CLASS_OF(obj);
                 if (RB_TYPE_P(klass, T_CLASS) && FL_TEST(klass, FL_SINGLETON)) {
-                    s = FAKE_CSTR(&s_str, "extended object ");
+                    s = FAKE_CSTR(&s_str, "");
+                    c = rb_any_to_s(obj);
+                    break;
                 }
                 else {
-                    s = FAKE_CSTR(&s_str, "object ");
+                    s = FAKE_CSTR(&s_str, "an instance of ");
+                    c = rb_class_real(klass);
                 }
-                c = rb_class_real(klass);
             }
             c2 = rb_protect(name_err_mesg_receiver_name, c, &state);
             if (state || NIL_OR_UNDEF_P(c2))