We were always rendering <symbol> SVG elements, but we should only
render them if they are a child of a <use>'s shadow root. This caused
practically all instances of <symbol> to be drawn at least one time too
many.
When an element has `display: contents` and it gets marked for a layout
tree rebuild, we actually have to mark its parent for rebuild as well.
The structure of the parent (and siblings) may change depending on how
the `display: contents` element changes (e.g position, display, etc.)
Otherwise the layout tree will still contain the top layer element(s).
Fixes Steam Events & Announcements `<dialog>` modal visually not fully
disappearing upon removal.
Inline nodes in our layout tree have a position, so let's show it. By
centralizing the logic for this, block nodes now lose their redundant
'content-size' dump info which is already part of the box model dump.
We were only dumping a PaintableBox' dimensions if its layout node was a
Layout::Box as well, causing us to not dump the dimensions of paintables
for inline nodes in the paintable tree.
When marking a part of the layout tree for rebuild, if the subtree root
that we're marking has an anonymous parent, we now mark from the nearest
non-anonymous ancestor instead.
This ensures that subtrees inside anonymous wrappers don't just get
duplicated (i.e recreated but inserted instead of replaced).
Browsers such as Chrome and Firefox apply an arbitrary scale to the
current font size if `normal` is used for `line-height`. Firefox uses
1.2 while Chrome uses 1.15. Let's go with the latter for now, it's
relatively easy to change if we ever want to go back on that decision.
This also requires updating the expectations for a lot of layout tests.
The upside of this is that it's a bit easier to compare our layout
results to other browsers', especially Chrome.
