Top-level `ORDER BY` does not seem to be applied to unions

MySQL
```
mysql> select 1000 union select 1 order by 1;
+------+
| 1000 |
+------+
| 1 |
| 1000 |
+------+
2 rows in set (0.00 sec)

mysql> select 1000 union (select 1 order by 1);
+------+
| 1000 |
+------+
| 1000 |
| 1 |
+------+
2 rows in set (0.00 sec)
```

Dolt
```
tmp/main*> select 1000 union select 1 order by 1;
+------+
| 1000 |
+------+
| 1000 |
| 1 |
+------+
2 rows in set (0.00 sec)

tmp/main*> select 1000 union (select 1 order by 1);
+------+
| 1000 |
+------+
| 1000 |
| 1 |
+------+
2 rows in set (0.00 sec)
```

No repository files or tests are named. Reproduce both UNION queries in Dolt and trace the SQL UNION and top-level ORDER BY handling, comparing the results with MySQL; done means both queries apply ordering as shown by MySQL and regression tests cover them.

Written by the indexing model from the issue text.