wasm-smith: Whitelist/blacklist for instructions

[ark0f]

Would it be worth adding an option to enable/disable generation of specific instructions?

[alexcrichton]

The crate currently supports "instruction classes" and enabling/disabling specific proposals, but not currently a per-instruction basis. Do either of these work for your use case? If not can you expand on why those aren't sufficient and per-instruction would be useful?