This patch adds support for the `SLINT_KMS_ROTATION` environment
variable, that instructs the Skia/FemtoVG renderers to rotate
the scene before rendering.
This doesn't require a windowing system, just Linux and Vulkan drivers
that supports the display extensions.
It's called linuxkms as soon this will go beyond Vulkan and also support
EGL and perhaps dumb buffers for software rendering.