Add lint and tests for unnecessary parens around types
This is my first contribution to the Rust project, so I apologize if I'm not doing things the right way.
The PR fixes#64169. It adds a lint and tests for unnecessary parentheses around types. I've run `tidy` and `rustfmt` — I'm not totally sure it worked right, though — and I've tried to follow the instructions linked in the readme.
I tried to think through all the variants of `ast::TyKind` to find exceptions to this lint, and I could only find the one mentioned in the original issue, which concerns types with `dyn`. I'm not a Rust expert, thought, so I may well be missing something.
There's also a problem with getting this to build. The new lint catches several things in the, e.g., `core`. Because `x.py` seems to build with an equivalent of `-Werror`, what would have been warnings cause the build to break. I got it to build and the tests to pass with `--warnings warn` on my `x.py build` and `x.py test` commands.
It would be nice to demonstrate the shining correctness here with more
run-rustfix tests than this, but unfortunately, that doesn't work with
multipart suggestions yet (#53934).
While we're here, reword the zero-use lifetime suggestion to "elide
the unused lifetime" instead of "remove it". (It's classier.)
