patch 9.0.1999: Vim9: some error messages can be improved

Problem:  Vim9: some error messages can be improved
Solution: Mention the defining class for variable access error message

closes: #13272

Signed-off-by: Christian Brabandt <cb@256bit.org>
Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Co-authored-by: Ernie Rael <errael@raelity.com>
diff --git a/src/vim9execute.c b/src/vim9execute.c
index a899745..f237132 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -2180,8 +2180,8 @@
 	    {
 		if (*member == '_')
 		{
-		    semsg(_(e_cannot_access_private_variable_str),
-						m->ocm_name, cl->class_name);
+		    emsg_var_cl_define(e_cannot_access_private_variable_str,
+							m->ocm_name, 0, cl);
 		    status = FAIL;
 		}