Implement `unbounded_shl`/`unbounded_shr`

These recent Rust integer methods semantically map cleanly onto OpShiftLeftLogical/OpShiftRightLogical.

This is in contrast to normal Rust shifts, whose semantic is such that shifting by the amount that is equal to or larger than number of bits in an integer is UB:

error: this arithmetic operation will overflow
 --> src/main.rs:3:20
  |
3 |     println!("{}", u32::MAX >> 32);
  |                    ^^^^^^^^^^^^^^ attempt to shift right by `32_i32`, which would overflow
  |
  = note: `#[deny(arithmetic_overflow)]` on by default

My understanding is that rust-gpu doesn't map these methods to those instructions yet, probably resulting in use of conditional logic from standard library, which is less efficient, at least without additional optimizations:

impl u32 {
    pub const fn unbounded_shr(self, rhs: u32) -> u32 {
        if rhs < Self::BITS {
            unsafe { self.unchecked_shr(rhs) }
        } else {
            0
        }
    }
}

Start by locating the Rust integer method lowering and the code paths that emit OpShiftLeftLogical and OpShiftRightLogical. Verify that unbounded_shl and unbounded_shr use those instructions directly, including shift amounts at or above the integer width, and add or update coverage for those cases.