\brief Score a given data-type involving a union against data-flow The data-type must either be a union or a pointer to union. Set up the initial set of trials based on the given data-flow edge (PcodeOp and slot). \param tgrp is the TypeFactory owning the data-types \param parentType is the given data-type to score \param op is PcodeOp of the given data-flow edge \param slot is slot of the given
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