[FTD] Extend HandshakeCombineSteeringLogic

[QinYuan2000]

This PR adds more simplification patterns for steering logic generated by FTD.

Main changes:

• Add a shared equivalence check for SSA values, constants, and NOT chains.
• Merge equivalent NotIOp, MuxOp, and ConditionalBranchOp.
• Remove double NOTs, and any MuxOp/ConditionalBranchOp/ConstantOp/SourceOp/NotIOp whose results are all unused.
• Replace branch conditions that are already known with constants.
• Short-circuit branches with a constant condition, and collapse muxes whose two data inputs are identical.
• Split mux-conditioned branches into nested branches to expose a mergeable outer branch.