Use tidy to enforce alphabetical dependency ordering

[nnethercote]

I get annoyed when dependencies in Cargo.toml files are not in alphabetical order. The style guide agrees with me.

There are ongoing efforts to provide linting/formatting of Cargo.toml files, e.g. rust-lang/rustfmt#5240, https://crates.io/crates/cargo-toml-lint, and https://github.com/TimonPost/cargo-toml-format. But it's far from clear what's the right approach.

So this PR does something very simple: it uses the order checking already present in tidy. This allows incremental application of ordering, starting right now, and avoiding the need for any kind of all-at-once conversion.

If we do end up using some more comprehensive Cargo.toml linting/formatting solution in the future, the tidy-alphabetical lines will be easy to remove.

r? @wesleywiser

[wesleywiser]

@bors r+ rollup

[bors]

📌 Commit 10ab51d has been approved by wesleywiser

It is now in the queue for this repository.

[bors]

⌛ Testing commit 10ab51d with merge c07693c...

[bors]

☀️ Test successful - checks-actions
Approved by: wesleywiser
Pushing c07693c to master...

[rust-timer]

Finished benchmarking commit (c07693c): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.9%	[-2.9%, -2.9%]	1
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 624.881s -> 625.421s (0.09%)
Artifact size: 305.58 MiB -> 305.57 MiB (-0.01%)