1. Stop using -1 to indicate infinity value of growth limit. Just use
INFINITY for that.
2. More complete implementation of "Expand Flexible Tracks" step.
3. Return AvailableSize from get_free_space: spec says that this
function can return indefinite size and it is ok.
The file template-areas.html, which previously had multiple grid tests,
has now been divided into smaller files, each containing only one grid
test. It is going to make it easier to identify what inputs have been
affected by changes in layout code.
Also this change removes parts of template-areas.html that we can't
layout correctly yet.
The current config on GitHub Actions does not use ccache, so it takes
quite a while to build. Instead, let's just run these tests on Azure
where we already build Ladybird and have ccache enabled. This also lets
us sanitize LibWeb on both Linux and macOS.
The script changes here are to A) handle differences between Azure and
GitHub Actions and B) to support running on macOS.
