Support RowMergedNumericTable as GPU Kmeans input dataset

[xwu99]

We used RowMergedNumericTable as GPU Kmeans input dataset. The code can work with CPU kernels but crash for GPU. The reason we used RowMergedNumericTable is that those input sub tables are pre-processed by different thread in discrete places and they are huge. It will cost a lot to move them into a consolidated NumericTable. I wonder if this sceneario can be supported for GPU kernels.

@PIVOVAR3AL @amgrigoriev

[xwu99]

#1712

[amgrigoriev]

Required functionality was added. Please see sycl examples for row merged numeric table in repository.