Support << left shift or >> right shift operator

[katat]

It is common to need to << or >> to manipulate a value via bit shifting.

Without bit shifting, it needs to do the following:

   // 1 << LEN
    let mut pow2 = 1;
    for ii in 0..LEN {
        pow2 = pow2 + pow2;
    }

The left hand side will be always the value, while the right hand side will be the number of bits to shift.

We can add a builtin to support this operator. For example, the compiler will call the newly added builtins corresponding to the following new binary operations.

pub enum Op2 {
    Addition,
    Subtraction,
    Multiplication,
    Division,
    Equality,
    Inequality,
    BoolAnd,
    BoolOr,
+   RightShift,
+   LeftShift,
}

To implement, it needs to take care two cases for the value being shifted:

• constant: When the value is a constant, then the builtin function just do the shifting operation and return the value.
• cell var: When the value is a cell var, the builtin needs to handle constraints.