Support Multiplication and Division in ZKWASM

[aborg-dev]

Right now Cranelift backend only supports addition and subtraction operations. We want to extend it to support multiplication and division.

An example program would be:

(module
 (import "env" "assert_eq" (func $assert_eq (param i32) (param i32)))
 (func $main
	i32.const 2
	i32.const 3
	i32.mul
	i32.const 6
	call $assert_eq)
 (start $main))

(and another similar one for division)

[nagisa]

Arbitrary multiplication seems like could be supported with the :ARITH instruction which is actually a add-multiply instruction, but we can always set the add component to zero.