Component bindgen fails when a parameter or field is named b #1940

host_bindgen! output doesn't compile when a WIT parameter or record field is named b:

package a:b;
world w { export f: func(a: u32, b: string) -> u32; }

error[E0608]: cannot index into a value of type `usize`
    let b_field = &r#b[b_cursor..];

The generated decoder stores byte counts in a local named b, for example at hl.rs#L64. The WIT name b becomes the identifier r#b, which is the same name, so the counter shadows the value. The same pattern appears in several other places in hl.rs.

The counters need names that can't collide with WIT names, for example derived from id as other temporaries are.