This PR fixes a bug in the handling of `@utility`. Essentially if you
had a declaration where you used a `--modifier(…)` _and_ a `--value(…)`
and both caused the declaration to be removed, the declaration after the
current one would be removed as well.
This happened because 2 reasons:
1. Once we removed the declaration when we handled `--modifier(…)`, we
didn't stop the walk and kept going.
2. The `replaceWith(…)` code allows you to call the function multiple
times but immediately mutates the AST. This means that if you call it
multiple times that you are potentially removing / updating nodes
followed by the current one.
E.g.:
```css
@utility mask-r-* {
--mask-right: linear-gradient(to left, transparent, black --value(percentage));
--mask-right: linear-gradient(
to left,
transparent calc(var(--spacing) * --modifier(integer)),
black calc(var(--spacing) * --value(integer))
);
mask-image: var(--mask-linear), var(--mask-radial), var(--mask-conic);
}
```
If this is used as `mask-r-10%`, then the first definition of
`--mask-right` is kept, but the second definition of `--mask-right` is
deleted because both `--modifier(integer)` and `--value(integer)` do not
result in a valid value.
However, the `mask-image` declaration was also removed because the
`replaceWith(…)` function was called twice. Once for
`--modifier(integer)` and once for `--value(integer)`.
# Test plan
1. Added a test to cover this case.
2. Existing tests pass.
3. Added a hard error if we call `replaceWith(…)` multiple times.
d698c10836