patch 8.2.3190: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move error messages to errors.h and give them a clear name.
diff --git a/src/list.c b/src/list.c
index 4b9236a..55b9fa0 100644
--- a/src/list.c
+++ b/src/list.c
@@ -3049,7 +3049,7 @@
 	}
 	else if (argvars[2].v_type != VAR_NUMBER)
 	{
-	    emsg(_(e_number_exp));
+	    emsg(_(e_number_expected));
 	    return;
 	}
 	else