[css-grid] Definition of fit-content() uses min()/max() wrong

In <https://drafts.csswg.org/css-grid/#valdef-grid-template-columns-fit-content>, the formula is stated as:

```
min(minimum, max(limit, max-content))
```

This is *not* how you clamp a value between a min and max; instead, it ensures that the result is *outside* of the min-max range. Need to swap the use of min() and max() there, or switch to a clamp() notation now that that's well-defined.