The main goal of this PR was to support canonicalization of zero like
values. We essentially want to canonicalize `-mt-0` as `mt-0`, but also
`mt-[0px]`, `mt-[0rem]`, and other length-like units to just `mt-0`.
To do this, we had to handle 2 things:
1. We introduced some more constant folding, including making `0px` and
`0rem` fold to `0`. We only do this for length units. We also normalize
`-0`, `+0`, `-0.0` and so on to `0`.
2. While pre-computing utilities in our lookup table, we make sure that
we prefer `mt-0` over `-mt-0` if both result in the same signature.
Moved some of the constant folding logic into its own function and added
a bunch of separate tests for it.
## Test plan
Added more unit tests where we normalize different zero-like values to
`0`.
Running the canonicalization logic:
```js
designSystem.canonicalizeCandidates([
'-m-0',
'-m-[-0px]',
'-m-[-0rem]',
'-m-[0px]',
'-m-[0rem]',
'm-0',
'm-[-0px]',
'm-[-0rem]',
'm-[0px]',
'm-[0rem]',
'm-[calc(var(--spacing)*0)]',
'm-[--spacing(0)]',
'm-[--spacing(0.0)]',
'm-[+0]',
'm-[-0]',
'-m-[-0]',
'-m-[+0]',
]) // → ['m-0']
```
---------
Co-authored-by: Jordan Pittman <jordan@cryptica.me>
01d1e98259