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.
This iterates the fragments of the containing block, and paints their
outlines if they are descendants of the InlineNode.
If multiple fragments are adjacent, eg:
```html
<span><b>Well</b> hello <i>friends!</i></span>
```
...then we get a double-thick outline between "Well", " hello " and
"friends!", but we can come back to this after we implement
non-rectangular outlines for the `outline` CSS property.
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 *
