Make ComputedValuesExt expose keywords for the sizing properties
This will allow callers to start obeying min-content, max-content,
fit-content and stretch in follow-up patches.
The old functionality is kept as deprecated methods that we should
eventually remove.
This patch has very little impact on the existing behavior, just some
very minimal implementation of the keywords for css tables.
This also overhauls fixed-layout-2.html since:
- It had code that wasn't doing anything
- It had wrong expecations in prose
- The logic seemed broken in general
- All browsers were failing one testcase
Signed-off-by: Oriol Brufau obrufau@igalia.com