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
        }
    }
}

Inizia individuando il lowering dei metodi per interi di Rust e i percorsi del codice che emettono OpShiftLeftLogical e OpShiftRightLogical. Verifica che unbounded_shl e unbounded_shr usino direttamente queste istruzioni, inclusi gli shift maggiori o uguali alla larghezza dell’intero, e aggiungi o aggiorna la copertura per questi casi.