Use tidy to sort `sym::*` items
Use tidy to sort the symbols in the invocation of `symbols!`, instead of implementing the ordering check inside the proc macro.
(asked `````@nnethercote````` about this on zulip, he didn't have any reservations about making this change)
This has a couple of benefits:
- tidy's "version sort" (thanks to rust-lang/rust#141311 !) is nicer than the naive-cmp sort, so, e.g. `AtomicI{8, 16, 32, 64, 128}` are properly sorted by bit width.
- consistency with the rest of the repo
- allows us to remove a bit of order-verifying code from the `symbols!` proc macro impl
7103bbb86a