In plasma code, it's more common to see `/** ... */` doxygen comments
rather than `/** ... **/`.
This change fixes up doxygen comment terminators to prevent inconsistency
issues.
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.
This rewrites the wl_seat protocol implementation to adhere to the new
design principles.
Effectively, we've been supporting wl_seat v7 so the version was also
bumped from 5 to 7.
