Function indy_sys::anoncreds::indy_prover_get_credentials_for_proof_req

#[no_mangle]
pub unsafe extern "C" fn indy_prover_get_credentials_for_proof_req(
    command_handle: CommandHandle, 
    wallet_handle: WalletHandle, 
    proof_request_json: CString, 
    cb: Option<ResponseStringCB>
) -> Error