Fix unused_parens false positive
Resolvesrust-lang/rust#143653.
The "no bounds exception" was indiscriminately set to `OneBound` for referents and pointees. However, if the reference or pointer type itself appears in no-bounds position, any constraints it has must be propagated.
```rust
// unused parens: not in no-bounds position
fn foo(_: Box<(dyn Send)>) {}
// unused parens: in no-bounds position, but one-bound exception applies
fn bar(_: Box<dyn Fn(&u32) -> &(dyn Send)>) {}
// *NOT* unused parens: in no-bounds position, but no exceptions to be made
fn baz(_: Box<dyn Fn(&u32) -> &(dyn Send) + Send>) {}
```
75ed6de1ee