patch 9.0.1123: class function not implemented yet

Problem:    Class function not implemented yet.
Solution:   Implement defining and calling a class function.
diff --git a/src/vim9expr.c b/src/vim9expr.c
index ba2c826..463e79c 100644
--- a/src/vim9expr.c
+++ b/src/vim9expr.c
@@ -587,7 +587,8 @@
 	}
 	else
 	{
-	    lvar_T lvar;
+	    lvar_T  lvar;
+	    class_T *cl = NULL;
 
 	    if (lookup_local(*arg, len, &lvar, cctx) == OK)
 	    {
@@ -602,6 +603,10 @@
 		else
 		    gen_load = TRUE;
 	    }
+	    else if (class_member_exists(name, &cl, &idx, cctx))
+	    {
+		res = generate_CLASSMEMBER(cctx, TRUE, cl, idx);
+	    }
 	    else
 	    {
 		// "var" can be script-local even without using "s:" if it