op_shl and op_shr API is unsafe in native backend

[illusory0x0]

https://en.cppreference.com/w/c/language/operator_arithmetic

The behavior is undefined if rhs is negative or is greater or equal the number of bits in the promoted lhs.

///|
pub fn Int::op_shl(self : Int, other : Int) -> Int = "%i32_shl"

///|
pub fn Int::op_shr(self : Int, other : Int) -> Int = "%i32_shr"

I recommend the following API

///|
pub fn Int::op_shl(self : Int, other : UInt) -> Int

///|
pub fn Int::op_shr(self : Int, other : UInt) -> Int

and if greater or equal the number of bits in the promoted lhs, I think we need to panic in all backend.

• Proposal: checked arithmetic operations for Int and Int64 #241