Fails to parse string starting with byte order mark

```rust
let string = "\u{feff}foo";
eprintln!("{:?}", string.parse::<TokenStream>());
```

proc_macro::TokenStream:

```console
Ok(TokenStream [Ident { ident: "foo", span: #6 bytes(31..42) }])
```

proc_macro2::TokenStream:

```console
Err(LexError { span: Span })
```