Detect invalid turbofish `foo.bar::Type<T>()`in the parser

[estebank]

Detect when the user has likely forgotten to wrap the type param with the type param delimiters:

fn main() {
    let _ = vec![1, 2, 3].into_iter().collect::Vec<_>();
}

where we currently emit:

error: expected one of `(`, `.`, `;`, `?`, or an operator, found `::`
 --> src/main.rs:2:46
  |
2 |     let _ = vec![1, 2, 3].into_iter().collect::Vec<_>();
  |                                              ^^ expected one of `(`, `.`, `;`, `?`, or an operator