The C# class-body walker only handled field_declaration, so a
property's type produced no references(field) edge. In idiomatic C#,
auto-properties (`public Widget Main { get; set; }`) — not bare fields
— are the standard way to declare state, so this silently dropped most
of a class's type relationships.
Add a property_declaration branch alongside the field_declaration
handler, guarded the same way (ts_module == tree_sitter_c_sharp,
parent_class_nid set). A property exposes its type on the node directly
(no variable_declaration wrapper), so read it via
child_by_field_name("type") and collect refs with
_csharp_collect_type_refs, mirroring the Java/PHP/Kotlin siblings so
List<Widget> yields both the List field ref and the Widget generic_arg
ref. Only emit when target != parent_class_nid.
