impl fold_const for TypeFreshener
impl fold_const for TypeFreshener

Signed-off-by: Gabriel Smith <81bf9ba0f03e0524e8363ab0b55760deec97bc99@gmail.com>

graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust