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.
Spec defines `[LegacyNullToEmptyString]` on `value` argument of
`setProperty` but since `internal_set` calls `setProperty` directly
instead of using IDL generated binding, we need to make sure that null
is treated as empty string.
Fixes items grid loading on https://d.rsms.me/stuff/
