Some subtests changed in response to this CSSWG resolution:
https://github.com/w3c/csswg-drafts/issues/11494#issuecomment-2675800489
Basically, `border-style: none` now affects the used value of
`border-width`, not the computed value. (And the same for `outline`
properties.)
This affects way more tests than I expected because
interpolation-testcommon.js now adds tests for composition.
We now also store `outline-width` in ComputedValues as a `CSSPixels`
since we know it's an absolute length at `apply_style` time - this saves
us some work in converting to CSSPixels during layout.
Gains us 46 new passes since we now interpolate keywords (thick, thin,
etc) correctly.
Also loses us 4 WPT tests as we longer clamp negative values produced by
interpolation from the point of view of getComputedStyle (although the
'used' value is still clamped).
Shorthand subproperties that match their initial values are now
excluded from serialization, by default.
Properties where this behavior is not desired, like `gap`, are
special-cased.
