Benefits:
- A TOML 1.0 compliant parser
- Unblock future work
- Have `cargo init` add the current crate to the workspace, rather
than error
- #5586: Upstream `cargo-add`
TODO
- [x] Analyze performance and address regressions
- [x] Identify and resolve incompatibiies
- [x] Resolve remaining test failures, see
https://github.com/ordian/toml_edit/labels/cargo
- [x] ~~Switch the code from https://github.com/rust-lang/cargo/pull/10176 to only parse once~~ (this PR is being merged first)