Currently the Workspace processes output updates as they occur, e.g.
when the drm backend scans connectors, the Workspace will handle
hotplugged outputs one by one or if an output configuration changes the
mode of several outputs, the workspace will process output layout
updates one by one instead of handling it in one pass. The main reason
for the current behavior is simplicity.
However, that can create issues because it's possible that the output
layout will be temporarily in degenerate state and features such as
sticking windows to their outputs will be broken.
In order to fix that, this change makes the Workspace process batched
output updates. There are several challenges - disconnected outputs have
to be alive when the outputsQueried signal is emitted, the workspace
needs to determine what outputs have been added or removed on its own.
Things such as Output, InputDevice and so on are made to be
multi-purpose. In order to make this separation more clear, this change
moves that code in the core directory. Some things still link to the
abstraction level above (kwin), they can be tackled in future refactors.
Ideally code in core/ should depend either on other code in core/ or
system libs.
Since both output-management-v2 protocol implementation and the rest of
kwin live in the same place and the fact that kde-output-management-v2
is very plasma specific, we can move Platform::requestOutputsChange() to
the implementation of kde-output-management-v2 protocol, it simplifies
the code a bit and improve code encapsulation.
In order to further simplify kde-output-management-v2 protocol, this
change alters the behavior of the protocol so an output configuration
can be applied only once, which is a very reasonable behavior.
