Add `database_api::get_next_object_id` API

PR for #2649.

This PR adds a database API which partially depends on the api_helper_indexes plugin.

get_next_object_id( space_id, type_id, whether_with_pending_transactions )

/**
 * @brief Get the next object ID in an object space
 * @param space_id The space ID
 * @param type_id The type ID
 * @param with_pending_transactions Whether to include pending transactions
 * @return The next object ID to be assigned
 * @throw fc::exception If the object space does not exist, or @p with_pending_transactions
 *                      is @a false but the api_helper_indexes plugin is not enabled
 */
object_id_type get_next_object_id( uint8_t space_id, uint8_t type_id,
                                   bool with_pending_transactions )const;

bitshares / bitshares-core

Add `database_api::get_next_object_id` API #2653