[IRSim] Treat Branch OperVals different from regular operands to ensure correct ordering

Branch operands are different from regular instructions. They can have a mix of boolean values and branch instructions. This makes sure that branches are treated as more of a special case and makes sure that the successor blocks are always in the same order, and that they do not include the conditional argument.

Reviewer: paquette
Differential Revision: https://reviews.llvm.org/D139337