We know that longhand values are always `StyleValueList`s
Introduces a new fail in the `view-timeline-shorthand.html` WPT test
but this is because the test is incorrect and we now correctly don't
contract when `view-timeline-inset` has dissimilar cardinality. See
web-platform-tests/wpt#56181
The remaining failing tests in view-timeline-shorthand.html are due to
either:
a) incorrect tests, see web-platform-tests/wpt#56181 or;
b) a wider issue where we collapse coordinating value list longhand
properties to a single value when we shouldn't.
The remaining failing tests in scroll-timeline-shorthand.html are due to
either:
a) incorrect tests, see web-platform-tests/wpt#56181 or;
b) a wider issue where we collapse coordinating value list longhand
properties to a single value when we shouldn't.
