This remained undetected for a long time as HeaderCheck is disabled by
default. This commit makes the following file compile again:
// file: compile_me.cpp
#include <LibWeb/CSS/GridTrackSize.h>
// That's it, this was enough to cause a compilation error.
Often in the spec they talk about intrinsic_track_sizes and this way can
have a clearer way of checking if a GridTrackSize is indeed an
"intrinsic track size".
Makes it more convenient to create auto GridTrackSizes. I think having
an auto GridTrackSize be defined by an auto Length value kind of
confusing, and this at least helps when creating one.
Use float instead of int for the GridTrackSize length value as
FlexibleLengths can be "1fr" as well as ".49fr" in grid-track-row
and grid-track-column values.
