Now that we build lines incrementally, we no longer need the atomic line
splitting API.
The new InlineLevelIterator and LineBuilder setup does have some
regressions from the old behavior, but we can deal with them as we go.
There's a subtle difference here. A "block box" in the spec is a
block-level box, while a "block container" is a box whose children are
either all inline-level boxes in an IFC, or all block-level boxes
participating in a BFC.
Notably, an "inline-block" box is a "block container" but not a "block
box" since it is itself inline-level.
In the past, the base class implementation of this was used to descend
into subtrees and paint children. That is now taken care of by
StackingContext::paint_descendants() instead, and nothing used this.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
This is required for the block formatting context to know the height of
the <br> element while computing the height of its parent. Specifically,
this comes into play when the <br> element is the first or last child of
its parent. In that case, it previously would not have any fragments, so
BlockFormattingContext::compute_auto_height_for_block_level_element
would infer its top and bottom positions to be 0.
