Function encode_partition_topdown

fn encode_partition_topdown<T: Pixel, W: Writer>(
    fi: &FrameInvariants<T>,
    ts: &mut TileStateMut<'_, T>,
    cw: &mut ContextWriter<'_>,
    w_pre_cdef: &mut W,
    w_post_cdef: &mut W,
    bsize: BlockSize,
    tile_bo: TileBlockOffset,
    block_output: &Option<PartitionGroupParameters>,
    inter_cfg: &InterConfig,
    enc_stats: &mut EncoderStats,
)