Implement the `dense` keyword for `grid-auto-flow` so auto-placed items
backfill earlier gaps in the grid. The sparse/dense cursor logic is now
centralized in `place_grid_items()` step 4: dense resets the cursor to
the grid start before each search, while sparse keeps advancing forward.
Also fix a pre-existing bug where `find_unoccupied_place()` and several
placement helpers only checked if a single cell was unoccupied, ignoring
multi-cell spans. Add `OccupationGrid::is_area_occupied()` and use it
throughout to correctly verify the entire rectangular area is available.
Introduce AbsposContainingBlockInfo and a virtual
resolve_abspos_containing_block_info() method on FormattingContext that
computes the containing block rect, per-axis positioning mode (static
position vs inset-from-rect), and optional grid alignment — all in one
place.
The base implementation handles the common case: padding-box rect of
the containing block, with inline containing block support. GFC
overrides it to return the grid area rect with alignment info.
This replaces the per-context abspos loops that BFC, FFC, TFC, and GFC
each had, with a shared layout_absolutely_positioned_children() +
layout_absolutely_positioned_element() pair. The offset computation is
simplified from ~40 lines of branching to a data-driven dispatch on the
axis mode, and GFC's ~130-line custom layout method is replaced by a
~30-line resolve override.
Not every user of this requires an `auto` state, but most do.
This has quite a big diff but most of that is mechanical:
LengthPercentageOrAuto has `resolved_or_auto()` instead of `resolved()`,
and `to_px_or_zero()` instead of `to_px()`, to make their output
clearer.
`collapse_auto_fit_tracks_if_needed()` had a check that does collapsing
only if auto-fit is used like
`grid-template-columns: repeat(auto-fit, 1px);`, and it didn't work for
valid cases when `repeat(auto-fit)` is placed in the middle of
definition like `grid-template-columns: 1px repeat(auto-fit, 1px) 1px;`.
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.
It was annoying to maintain two separate but almost identical functions
that gradually accumulated small differences over time. This change
replaces them with a single function that resolves either width or
height, depending on the specified dimension.
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
