This PR improves the codemod tool to simplify 2 things:
1. Whenever you have a `theme(…)` call, we try to change it to a
`var(…)`, but if that doesn't work for some reason, we will make sure to
at least convert it to the more modern `--theme(…)`.
2. When converting `theme(spacing.2)`, we used to convert it to
`calc(var(--spacing)*2)`, but now we will convert it to `--spacing(2)`
instead.
82589eb2c1