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.
There are some nuances to creating these wrappers, such as manually
propagating certain text styles that are not inherited by default. We
already have the logic for this in
`NodeWithStyle::create_anonymous_wrapper()`, so reuse that method in our
implementation of the button layout.
Fixes applying certain text styles (such as `text-decoration`) to the
text of a `<button>`.
