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/reader/src/lexer.rs

@@ -381,7 +381,7 @@ impl<'a> Lexer<'a> {
         };
         if is_vector {
             if number <= u32::from(u16::MAX) {
-                base_type.by(number as u16).map(Token::Type)
+                base_type.by(number).map(Token::Type)
             } else {
                 None
             }