DmdAnal: Look through unfoldings of DataCon wrappers (#22241)

Previously, the demand signature we computed upfront for a DataCon wrapper

lacked boxity information and was much less precise than the demand transformer

for the DataCon worker.

In this patch we adopt the solution to look through unfoldings of DataCon

wrappers during Demand Analysis, but still attach a demand signature for other

passes such as the Simplifier.

See `Note [DmdAnal for DataCon wrappers]` for more details.

Fixes #22241.