[flang] Fix problems with constant arrays with lower bounds that are not 1

There were two problems with constant arrays whose lower bound is not 1.
First, when folding the arrays, we were creating the folded array to have lower
bounds of 1 but, we were not re-adjusting their lower bounds to the
declared values.  Second, we were not calculating the extents correctly.
Both of these problems led to bogus error messages.

I fixed the first problem by adjusting the lower bounds in
NonPointerInitializationExpr() in Evaluate/check-expression.cpp.  I wrote the
class ArrayConstantBoundChanger, which is similar to the existing class
ScalarConstantExpander.  In the process of implementing and testing it, I found
a bug that I fixed in ScalarConstantExpander which caused it to infinitely
recurse on parenthesized expressions.  I also removed the unrelated class
ScalarExpansionVisitor, which was not used.

I fixed the second problem by changing the formula that calculates upper bounds
in in the function ComputeUpperBoun...