Replace the previous caching/binary-search approach with
Newton-Raphson iteration and bisection fallback. This is the
same algorithm used by WebKit, Chromium, and Firefox.
The old code had a broken binary search comparator that could never
return 0 (the second condition was always true when the first was
false), leading to out-of-bounds vector accesses and crashes.
Fixes#3628.
This excludes `step-end` and `step-start` which are expected to be
converted to the equivalent function at parse time.
We are expected to serialize these as the explicit keywords - previously
we would parse as `EasingStyleValue` and serialize equivalent functions
as the keywords. This caused issues as we would incorrectly serialize
even explicit functions as the keyword.
This also allows us to move the magic easing functions to
`EasingFunction` rather than `EasingStyleValue` which is a bit tidier
Previously we were doing this ad-hoc later in the process but we now
have the `calc` clamping system which can simplify things.
This reveals some false-positives in that we don't handle relative
lengths within these `calc`s but these are fixed in the next commit
Canonicalization can require information that is only known after
compute time (i.e. resolved relative lengths within calcs).
This also allows us to get rid of the `had_explicit_input` flag and just
rely on whether Optional has a value
