--value(…) usage is required in functional utilities

Otherwise if you don't do that:
```css
@Utility foo-* {
  color: red;
}
```

Then `foo-a`, `foo-b`, and `foo-c` will resolve to:
```css
.foo-a {
  color: red;
}
.foo-b {
  color: red;
}
.foo-c {
  color: red;
}
```

Which seems useless because this creates unnecessary duplicate CSS.

Author: RobinMalfait

packages/tailwindcss/src/utilities.ts

@@ -6233,8 +6233,9 @@ export function createCssUtility(node: AtRule) {
           node.value = ValueParser.toCss(valueAst)
         })
 
-        // Used `--value(…)` but nothing resolved
-        if (usedValueFn && !resolvedValueFn) return null
+        // Functional CSS utilities require `--value(…)`, and one of those
+        // branches must resolve for the candidate to be valid.
+        if (!usedValueFn || !resolvedValueFn) return null
 
         // Used `--modifier(…)` but nothing resolved
         if (usedModifierFn && !resolvedModifierFn) return null