Get slices to index a flat array for all source-receiver pairs.
Warning
Survey objects are mutable objects. If the sources or receivers in
it get modified, slices generated with this method will not match
the arrays linked to the modified survey.
Dictionary with flat array slices for every pair of source and
receiver in the survey. The keys are tuples of a single source and
a single receiver, and the values are the corresponding slice for
each one of them.
