This header has always been fundamentally a Kernel API file. Move it
where it belongs. Include it directly in Kernel files, and make
Userland applications include it via sys/ioctl.h rather than directly.
In case of possible framebuffer mapping overflow, just fallback to the
safe mode-setting of the DisplayConnector, because in that state we know
for sure that we can map a usable framebuffer (otherwise it is a bug in
the Kernel, and not WindowServer).
This value will be used later on by WindowServer to reject resolutions
that will request a mapping that will overflow the hardware framebuffer
max length.
All DisplayConnectors should support the mmap interface and it should
provide better performance now, so let's just use it and drop support
for the DisplayConnector's write interface from the WindowServer side.
This ioctl is more appropriate when the hardware supports flushing of
the entire framebuffer, so we use that instead of the previous default
FB_IOCTL_FLUSH_HEAD_BUFFERS ioctl.
The ScreenBackend is a thin wrapper around the actual screen hardware
connection. It contains all the variables specific to that hardware and
abstracts away operations that deal with controlling the hardware. The
standard ScreenBackend implementor is HardwareScreenBackend, which
contains all the existing frame buffer & ioctl handling code of Screen.
I took this opportunity to introduce ErrorOr wherever sensible.
