Nobody makes undefined Lengths now, (although actually removing
Undefined will come in a later commit) so we can remove this parameter,
and `resolved_or_auto()`/`resolved_or_zero()`.
Most of the time, we cannot resolve a `calc()` expression until we go to
use it. Since any `<length-percentage>` can legally be a `calc
()`, let's store it in `LengthPercentage` rather than make every single
user care about this distinction.
Despite looking like it was still needed, it was only used for passing
to other calls to Length::resolved() recursively. This makes the
various `foo.resolved().resolved()` calls a lot less awkward.
(Though, still quite awkward.)
I think we'd need to separate calculated lengths out to properly tidy
these calls up, but one yak at a time. :^)
This reimplements image tiling instead of using `Painter::blit_tiled()`,
so that we will be able to handle CSS's more complicated repetition
rules. (Like `background-repeat: space`) Otherwise this does the same as
before. :^)
Previously, a `background-repeat` value of `no-repeat` in a direction
would cause the image to be drawn at exactly that size. This was fine if
the image was smaller than the element, but if it was larger, it would
draw outside its bounds. Now, it behaves itself. :^)
