The cast expression expected any type via types::type_() function,
but the language spec does only allow TypeNoBounds (types without direct extra bounds
via `+`).
**Example:**
```rust
fn test() {
6i8 as i32 + 5;
}
```
This fails, because the types::type_() function which should parse the type after the
as keyword is greedy, and takes all plus sign after path types as extra.
My proposed fix is to replace the not implemented `type_no_plus()` just calls (`type_()`)
function, which is used at several places. The replacement is `type_with_bounds_cond(p: &mut Parser, allow_bounds: bool)`, which passes the condition to relevant sub-parsers.
This function is then called by `type_()` and the new public `type_no_bounds()`.
