SPR1-1944 Ensure unique out_name in get_dask_array
SPR1-1944 Ensure unique out_name in get_dask_array

The latest dask is unhappy if out_name == array_name like before.
During graph optimization the entire graph is culled. Embellish the
`out_name` by adding a deterministic hash to `array_name`.

Rename the new `getem` to `_graph_from_chunks` since it is more
descriptive and also since its interface differs from the function
it wraps anyway (`graph_from_arraylike`).

ska-sa/katdal