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

[tabatkins]

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.