The VM bytecode toString() function does not work when certain instructions are present (fillEmptyConst, getFieldConst, traversePConst, traverseFConst, and others). This is because the instruction pointer does not advance correctly. We should fix this, and add a sanity test for toString().

https://github.com/mongodb/mongo/blob/6bd5618937542267553791332394c571973740eb/src/mongo/db/exec/sbe/vm/vm.cpp#L175