CSS rules were storing absolute rather than relative line numbers (this
was done to match the old style system).

So when we hit the cached inline stylesheet code-path, for which we
share the CSS rules of the stylesheet, for the cache hit the line
numbers were completely off.

This particular page was probably regressed by bug 1834081, but the
issue could happen before with Shadow DOM.

Always store relative numbers and convert to absolute when asked by the
inspector, rather than the other way around.

This is simpler and makes the cache work.