Currently, we ues `#root` vs `#root > *` selector for component roots
depending on the number of root children. This heuristic detects
fragments that render multiple elements inside the root.
However, this does not work with empty fragments that do not render
anything.
The fix is to make the `#root >> control=component` selector that would
dynamically detect the root. This supports empty fragments and also
allows for dynamic updates of the fragments.
f17d345ac9