Since the Screens class is a convenience wrapper around AbstractOutput
objects that come from the Platform, it should not be platform-specific.
By dropping createScreens(), output-related code becomes simpler.
The main advantage of SPDX license identifiers over the traditional
license headers is that it's more difficult to overlook inappropriate
licenses for kwin, for example GPL 3. We also don't have to copy a
lot of boilerplate text.
In order to create this change, I ran licensedigger -r -c from the
toplevel source directory.
This is a very interesting auto test as Screens uses both Workspace
and Client. Thus it operates in the "impossible to mock" area.
The solution is to provide mock includes in autotests and ensure that
when building the auto-test the mock header includes will be picked
first. There is now a mock class for Workspace and Client providing
just the API pieces used inside Screens.
As Screens is abstract and we cannot properly interact with
QDesktopWidget there is also a MockScreens class inheriting from Screens
and mocking the required functionality (by just operating on a list of
QRects).
The auto-test itself is only performing checks on the abstract class.
The mock class is indirectly tested by Screens calling into the virtual
methods. The test case is not yet complete, but looking quite good
already.
