Parse subgrid track listings for grid-template rows and columns,
including fixed and auto-fill name-repeat line-name lists. Preserve
the subgrid keyword through computed values and shorthand serialization,
and make interpolation discrete instead of routing subgrid lists through
the explicit track interpolation path.
Import WPT coverage for subgrid grid-template parsing and computed
values, and add text coverage for discrete subgrid track-list animation.
This simplifies handling (particularly around absolutization and
interpolation) and allows us to support calculated flex values (which
will come in a later commit).
`grid-template-rows: fit-content(100px)` had no effect when the grid
container lacked an explicit height, because the fit-content growth
limit clamping was gated behind `available_size.is_definite()`.
Fix by normalizing fit-content tracks with unresolvable percentage
arguments to max-content during track initialization, then applying
the fit-content clamp unconditionally.
Fixes https://github.com/LadybirdBrowser/ladybird/issues/7730
This has always been a bit of a hack. Initially it made sense as a lot
of properties that accept a length also accept `auto`, but while
convenient, that leads to problems: It's easy to forget to check if a
length is `auto`, and places that don't accept it end up with an
invalid state lurking in the type system, which makes things unclear.
Reimplements `grid`, `grid-template`, `grid-template-rows`, and
`grid-template-columns` in a way that uses a separate function for each
grammar rule defined in the specification. This change results in many
additional passing tests from the already imported WPT suite. Most of
the remaining test failures are related to incorrect serialization of
grid properties.
