Use u32 in Type API (#4280)

Move from passing and returning u8 and u16 values to u32 in many of
the functions. This removes a number of type conversions and gives
a small compilation time speedup, around ~0.7% on my aarch64 machine.

Copyright (c) 2022, Arm Limited.

cranelift/codegen/src/bitset.rs

@@ -37,7 +37,7 @@ where
     }
 
     /// Check if this BitSet contains the number num
-    pub fn contains(&self, num: u8) -> bool {
+    pub fn contains(&self, num: u32) -> bool {
         debug_assert!((num as usize) < Self::bits());
         debug_assert!((num as usize) < Self::max_bits());
         self.0.into() & (1 << num) != 0