Support a Column of Arrays in UDTFs

[pearu]

The following example should be supported:

@omnisci('int32(Column<Array<double>>, RowMultiplier, Column<double>)')
def array_sum(x, m, y):
    for i in range(x):
        y[i] = sum(x[i])

[pearu]

An attempt is made in https://github.com/omnisci/omniscidb-internal/tree/pearu/array-column but according to Slack discussion https://quansight.slack.com/archives/CHSDG1C9W/p1613589094079000 the columnarization of columns of arrays will be problematic due to inflexibilities in ColumnarResult. So, the issue is put to hold.