By commenting out the parameter name, we get compile-time checks
Also, we can omit them for slots and Qt will not forward the parameters.
In case we had TODOs next to the code, I kept the Q_UNUSED statements
for now.
The rationale is explained in https://planet.kde.org/friedrich-kossebau-2023-06-28-include-also-moc-files-of-headers/
In case of KDEConnect, it impressively speeds up compilation. Before it
took 390 seconds on a clean build and with this change it took 330 seconds.
This is due to the mocs_compilation having to include the header files
and thus all their headers. Due to the lots of small plugins we have,
this means that the same headers must be compiled plenty of times.
When we include the moc files directly in the C++ file, they are already
available.
We've had separate title & artist for a while, and all clients should be
using those by now.
Also fixes the position change not being emitted when the song changes,
and fixes the values being written after emitting that they changed.
