Use StyleValue's computational-independence predicate when deciding
which specified values to retain for inherited-style recomputation.
Compound values such as shadows, filters, lists, and calc trees now
reuse their existing dependency tracking instead of the old bare-length
check.
Treat missing tuple entries and keyword-only edge offsets as
computationally independent. These nullable slots are part of the
parsed value representation, and the inherited dependency tracking now
uses the shared computational-independence query for specified values.
Add viewport resize coverage for media query changes that update root
font metrics while a descendant uses font-relative lengths inside
box-shadow and filter values.
Many CSS grammars call for us to parse `Foo || Bar` but we don't have a
good way to represent this unless we have a custom style value. Usually
we store the values in a `StyleValueList` but since that can only store
non-null elements we have to manually recheck which elements we have at
which index whenever we use it.
This style value holds a Vector of `RefPtr<StyleValue const>` so that we
can represent null values and know what values are at what index without
manually rechecking.
