This commit introduces proper handling of three intrinsic size keywords
when used for CSS heights:
- min-content
- max-content
- fit-content
This necessitated a few plumbing changes, since we can't resolve these
values without having access to containing block widths.
This fixes some visual glitches on https://www.supabase.com/ as well
as a number of WPT tests. It also improves the appearance of dialogs.