Add AlgebraicSimplifier pass directly in front of HloConstantFolding.
Add AlgebraicSimplifier pass directly in front of HloConstantFolding.

We have cases with DynamicSlice(Broadcast) which can be simplified away which
would otherwise be constant folded. The HloEvaluator is really slow for
DynamicSlice and Slice, as it will evalute the whole first operand, so if we
can simplify it away, it will help.
