Macro impl_v_ext

macro_rules! impl_v_ext {
    (
        $tag:ty,
        $field:ident,
        $product:ty,
        $asset:ty,
        $rational:ty,
        $time:ty,
        $addon:ty
    ) => { ... };
}

Implements VirtualDynExtension for a ProductType extension field.

Maps an extension discriminant to the virtual field, with layout defined by VirtualDynExtensionSchema via ProductProvider.