Adjust span of fn argument declaration
Span of a fn argument declaration goes from:
```
fn foo(i : i32 , ...)
^^^^^^^^
```
to:
```
fn foo(i : i32 , ...)
^^^^^^^
```
That is, we don't include the extra spacing up to the trailing comma, which I think is more correct.
cc https://github.com/rust-lang/rust/pull/99646#discussion_r944568074
r? ``@estebank``
---
The two tests that had dramatic changes in their rendering I think actually are improved, though they are kinda poor spans both before and after the changes. 🤷 Thoughts?
e369ec871e