Integrate `Property` with the `GodotConvert` API

[lilizoey]

In #421 we didn't integrate Property with the new API. This was to limit scope, however it means we now have a bunch of repeated effort since both Property and ToGodot/FromGodot both do conversions in different ways.

Property should instead be changed to using ToGodot and FromGodot as their conversion methods.

There is a derive macro for Property and that macro should likely be merged with the ToGodot and FromGodot derive macros, see #452.