Fix inconsistent symbol mangling of integers constants with -Zverbose
The `PrettyPrinter` changes formatting of array size and integer
constants based on `-Zverbose`, so its implementation cannot be used in
legacy symbol mangling.
Example symbol demangling before changes:
```console
$ cat a.rs
pub struct A<T>(T);
impl A<[u8; 128]> { pub fn f() {} }
$ rustc --crate-type=lib a.rs -Zverbose=n && nm -C ./liba.rlib
00000000 T a::A<[u8; 128]>::f
$ rustc --crate-type=lib a.rs -Zverbose=y && nm -C ./liba.rlib
00000000 T a::A<[u8; Const { ty. usize, val. Value(Scalar(0x0000000000000080)) }]>::f
```
c531b01e9d