Dead Code Analysis has too many hard coded features (Need features from `BranchOpInterface`)

- Has an ad hoc constant folder (`getOperandValues` and `getLiteralConstant?`)
- `isBranchOp` and `getSuccessorForOperands?` should be replaced with a proper interface like something in `ControlFlowInterfaces.lean` which should look similar to that of https://github.com/llvm/llvm-project/blob/main/mlir/include/mlir/Interfaces/ControlFlowInterfaces.td

It's been a while and I need to remind myself what the purpose of `getSuccessorForOperands` is for and how it should be used in the interface instead of hard coded in dead code. And I need a way to query for if an op is a branch op. The constant folder switch should be simpler - just use John's work and remove my hard coded stuff.