Currently this method always succeeds, but that won't be true once we
switch to the Core::Stream API. :^)
Some of these places would ideally show an error message to the user,
since failure to save a file is significant, but let's not get
distracted right now.
We create a base class called GenericFramebufferDevice, which defines
all the virtual functions that must be implemented by a
FramebufferDevice. Then, we make the VirtIO FramebufferDevice and other
FramebufferDevice implementations inherit from it.
The most important consequence of rearranging the classes is that we now
have one IOCTL method, so all drivers should be committed to not
override the IOCTL method or make their own IOCTLs of FramebufferDevice.
All graphical IOCTLs are known to all FramebufferDevices, and it's up to
the specific implementation whether to support them or discard them (so
we require extensive usage of KResult and KResultOr, together with
virtual characteristic functions).
As a result, the interface is much cleaner and understandable to read.
If a screen layout cannot be applied, instead of failing to start
WindowServer try to fall back to an auto-generated screen layout with
the devices that are detected.
Also, be a bit smarter about changing the current screen layout.
Instead of closing all framebuffers and bringing them back up, keep
what we can and only change resolution on those that we need to change
them on. To make this work we also need to move away from using an
array of structures to hold compositor related per-screen data to
attaching it to the Screen itself, which makes re-using a screen much
simpler.
This sets the stage so that DisplaySettings can configure the screen
layout and set various screen resolutions in one go. It also allows
for an easy "atomic" revert of the previous settings.
