Intrinsic sizing keywords weren't working correctly on the min and max
block sizes of a flex container, because we weren't setting the
`CacheableLayoutResult::content_block_size` to the right value. This
also ensures that `align-content` aligns within the final size of the
container.
Note it's not very clear what to do for single-line containers, they are
being discussed in https://github.com/w3c/csswg-drafts/issues/12123
Testing: Adding new WPT tests. There are still some failures, but most
subtests would fail without this change.
Fixes: #36981
Signed-off-by: Oriol Brufau <obrufau@igalia.com>
