...elements. Adds missing pseudo-element type passed into computed
properties getter.
Previously, due to this bug, we were using the element's computed
properties as the previous computed properties for its pseudo-elements.
This caused an excessive number of unintended CSS transitions to run.
The issue was particularly noticeable in Discord's emoji picker, where
each emoji has `::after` pseudo-element. We were incorrectly triggering
transitions on all their properties, resulting in significant
unnecessary work in style computation and animation event dispatching.
As the parser was trying to directly unwrap an unresolved duration.
Currently we are outputting the wrong results for the serialized
duration, but this is still a step forwards.
Fixes a crash seen on: https://evaparish.com/blog/how-i-edit
