There's no point for using the d-pointer pattern because the importer
and the exporter classes are private already, they are not exposed in
public api.
Currently, we have a mix of Frameworks versions and Plasma versions in
@since tags, which leads to some confusion. Since this is an unstable
library, one cannot rely on since version tags, we are free to add,
change, and remove apis to serve best to kwin requirements. Thus, we can
simply remove all since version tags to fix mixing up different product
versions.
The main reason why we have factory methods is that up to some point,
kwayland had its own signal to indicate when globals have to be removed.
Now that all globals add destroy listeners for the wl_display object,
we don't have that signal. Most factory methods are equivalent to doing
new T(display).
Besides adding unnecessary boilerplate code, another reason to get rid
of the factory methods is to reduce the amount of merge conflicts. If
several persons work on implementing wayland protocols at the same time,
sooner or later someone will have to resolve merge conflicts in Display.
