Mixing qt wayland versions can cause protocol errors if internal protocol extensions are used

This can happen if some applications are statically linked or some 3rd party decided to implement one of our internal protocols.

Since we have updated the internal protocols in backwards incompatible ways without renaming the protocols, it's now possible for a client to have a different definition of the protocols. I.e. with a different number of arguments for some request or events, causing protocol errors.

We should adopt a pattern where we rename the protocol if we make backwards incompatible changes. And also make it more clear that the internal protocols are internal, so other people will not rely on them without knowing they might be removed or renamed in the future.