Remote outputs and local output, buffer size combined in Maynard/GTK

While doing some Maynard tests with some WIP branch that add remote output support I've noticed some protocol errors/violations. The problem seem to reside in the toolkit as the client keeps committing with an older buffer size dimensions.

I also think tests with multiple outputs should be made, I think it might reveal the same issue. (Multiple outputs mean multiple connectors hooked up to the machine that runs the compositor/maynard).

Anyway, testing out remote outputs should be easy by adding something like the following

[remote-output]
name=transmitter_1
mode=800x600@60
host=192.168.100.9
port=34400

Starting maynard should see that it goes further with a libwayland error, which is caused by the fact that compositor tells the client to use a (new) surface size dimension, the client sends back a request that it acks that, but the buffer size is using both the local and the remote output dimensions as the buffer size (assumption is that it pretty much tries to use spawn the background entirely on both outputs).

Management data

This section is for management only, it should be the last one in the description.

Phabricator link: https://phabricator.apertis.org/T7514