Add ActionBuilder trait

[hikikones]

Make building a list of actions more explicit with the ActionBuilder trait. Start building a list by calling the ModifyActions::builder method, and submit with ActionBuilder::submit which returns the type for modifying actions again.

commands.actions(entity)
    // Modify actions as normal
    .add(action)
    // Make a list of actions
    .builder()
    .config(AddConfig {
        order: AddOrder::Front,
        start: false,
        repeat: false,
    })
    .push(action)
    .push(action)
    .push(action)
    .reverse()
    .submit()
    // Modify actions as normal again
    .add(action)
    .next()
    .clear()
    // ...