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
        }
    }
}

Comienza localizando el lowering de los métodos de enteros de Rust y las rutas de código que emiten OpShiftLeftLogical y OpShiftRightLogical. Verifica que unbounded_shl y unbounded_shr usen esas instrucciones directamente, incluidos los desplazamientos mayores o iguales al ancho del entero, y añade o actualiza la cobertura para esos casos.