Auto merge of #10338 - mkrasnitski:synthetic-params, r=flip1995

Ignore synthetic type parameters for `extra_unused_type_parameters`

There was a minor bug around calculating spans when forming the help message. An example:

```rust
fn unused_opaque<A, B>(dummy: impl Default) {}
//               ^^ ^
```

In this case, the entire list of generics should be highlighted, instead of each individual parameter. The culprit is the `impl Default`, which registers as a type parameter but doesn't live within the `<...>`. Because synthetic parameters can't ever be manually created, we just ignore them for this lint.

r? `@flip1995`
changelog: none
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0 files changed, 0 insertions, 0 deletions