Interpolation can leave `padding-*` values as negative - this should be
handled by interpolation clamping it to the allowed range of values
but we don't yet do that. As a stop gap we can clamp this before setting
it in ComputedValues.
This fixes 3 crashes and gains us 11 passes in the imported WPT tests
Before this change, we'd skip storing the new ComputedProperties in
Element::recompute_style() if there was no invalidation needed.
This caused us to lose the information about which properties are
inherited and/or important (which is also carried by ComputedProperties,
but doesn't affect invalidation).
Consequently, we'd then fail to recompute inherited styles, since that
mechanism depends on this data.
The fix is simply to always store the new ComputedProperties.
