Function safe_app::ffi::immutable_data::idata_serialised_size

#[no_mangle]
pub unsafe extern "C" fn idata_serialised_size(
    app: *const App, 
    name: *const XorNameArray, 
    published: bool, 
    user_data: *mut c_void, 
    o_cb: extern "C" fn(user_data: *mut c_void, result: *const FfiResult, serialised_size: u64)
)

Get serialised size of ImmutableData.