Add Wasmer (Singlepass) and Wasmer (Cranelift) to differential fuzzing infrastructure

[Robbepop]

Blocked by: #896, #894

Currently our differential fuzzer only supports Wasmi (register), Wasmi (stack) and Wasmtime.

In #894 we found out that adding both Wasmer (Singlepass) and Wasmer (Cranelift) might be beneficial in finding out if a found difference between the supported engines stems from Wasm based non-determinism since Wasmer (Cranelift) works more similar to Wasmtime and Wasmer (Singlepass) works more similar to Wasmi (register).

In supporting both Wasmer based backends we have more information to decide in these situation if such a find is a false positive.