[css-grid-1] Spanning items increase doesn't handle min-content maximums

[fantasai]

In “Increase sizes to accommodate spanning items content-sized tracks”, we handle

1. auto minimums
2. min-content minimums
3. max-content minimums
4. auto maximums
5. max-content maximums

It seems, however, that we don't handle the delta between an item’s auto and min-content contributions when min-content is specified as a maximum. :(

[Loirooriol]

Dupe of #4790

[fantasai]

There's no such thing as an auto maximum, actually. This error was introduced when we dfn'ed “min-size contribution” f48098c and needs to be reverted.