Add location of variable creation to attributes of symbol tale

Additionally store position of the end of the declaration instruction so that
when searching a symbol in a table one also check that the declaration point has
been passed.

This fix issues generated by the storage of symbol tables within node
description. The following code is now interpreted correctly

``
Z x = 1;
{
  Z x = x + 1;
  cout << x << "\n";
}
cout << x << "\n";
``

It now produces the expected output

``
2
1
``