Fixes to union properties

[packyg]

• Fix indentation of transforms on inner_propertys of the UnionProperty
  • Was overindented, causing error in generated models
• Update transform on all templates to take in a declare_type kwarg (default True) that determines if the first declaration of the property should include typedef
  • Used by union_property.pyi's transform to prevent mypy issues when calling the transform of its inner_properties
• Update construct on all templates to take a initial_value kwarg (defaults as appropriate, usually None, [] for lists)
  • Used by union_property.pyi's construct to prevent invalidly assigning None to the inner_property
• Update the _parse_<inner_property> function in union_property's construct to use the passed subresource instead of the top level dict from the outer scope