This is a part of refactoring towards making the paintable tree
independent of the layout tree. Now, instead of transferring text
fragments from the layout tree to the paintable tree during the layout
commit phase, we allocate separate PaintableFragments that contain only
the information necessary for painting. Doing this also allows us to
get rid LineBoxes, as they are used only during layout.
This patch makes a few changes to the way we calculate line-height:
- `line-height: normal` is now resolved using metrics from the used
font (specifically, round(A + D + lineGap)).
- `line-height: calc(...)` is now resolved at style compute time.
- `line-height` values are now absolutized at style compute time.
As a consequence of the above, we no longer need to walk the DOM
ancestor chain looking for line-heights during style computation.
Instead, values are inherited, resolved and absolutized locally.
This is not only much faster, but also makes our line-height metrics
match those of other engines like Gecko and Blink.
Before, we completely ignored clearance for block-level boxes if they
were floated. This was incorrect because it is valid for a block-level
box to be floated and still have clearance. However, unlike clearance
on normal flow boxes, clearance on floating boxes does not affect the
y-position of subsequent normal flow boxes. Instead, it pushes the
box's position to the very beginning of an edge.
Work towards https://github.com/SerenityOS/serenity/issues/21023
