Accept XMLOMIT attribute on structures

The XMLOMIT attribute is currently not accepted on structures.

The following declaration

dcl
1 a,
2 b xmlomit,
3 part1,
4 d1 fixed bin init(0),
4 d2 fixed bin init(0),
3 part2,
4 d1 fixed bin init(1),
4 d2 fixed bin init(0),
2 last fixed bin init(999);

would mean that substructure b is optional, but none of its children are.

So, either the whole substructure can be omitted (B and all its children) if all of its children are empty, or the whole substructure must be present if any of B child is not empty.

and the output should be

<A>
<B>
<PART1>
<D1>0</D1>
<D2>0</D2>
</PART1>
<PART2>
<D1>1</D1>
<D2>0</D2>
</PART2>
</B>
<LAST>999</LAST>
</A>

With the following declaration

dcl
1 a,
2 b xmlomit,
3 part1,
4 d1 fixed bin init(0),
4 d2 fixed bin init(0),
3 part2,
4 d1 fixed bin init(0),
4 d2 fixed bin init(0),
2 last fixed bin init(999);

the output would be

<A>
<LAST>999</LAST>
</A>

With the following declaration

dcl
1 a,
2 b xmlomit,
3 part1 xmlomit
4 d1 fixed bin init(0),
4 d2 fixed bin init(0),
3 part2,
4 d1 fixed bin init(1),
4 d2 fixed bin init(0),
2 last fixed bin init(999);

the output would be

<A>
<B>
<PART2>
<D1>1</D1>
<D2>0</D2>
</PART2>
</B>
<LAST>999</LAST>
</A>