[flang][acc] remap symbol appearing in reduction clause (#168876)
This patch is a follow-up of #162306 for the reduction clause.
Inside the compute region that carries the reduction clause, a new
hlfir.declare is generated for symbol appearing in the reduction clause.
The input of this hlfir.declare is the acc.reduction result. The related
semantics::Symbol is remapped to the hlfir.declare result so that any
reference to the symbol inside the compute region will use this SSA
value as the starting point instead of the SSA value for the host
address.
