LibGL+LibGPU+LibSoftGPU: Implement and expose glClipPlane

This commit implements glClipPlane and its supporting calls, backed
by new support for user-defined clip planes in the software GPU clipper.

This fixes some visual bugs seen in the Quake III port, in which mirrors
would only reflect correctly from close distances.

Userland/Libraries/LibGPU/Device.h

@@ -61,6 +61,7 @@ public:
     virtual void set_light_state(unsigned, Light const&) = 0;
     virtual void set_material_state(Face, Material const&) = 0;
     virtual void set_stencil_configuration(Face, StencilConfiguration const&) = 0;
+    virtual void set_clip_planes(Vector<FloatVector4> const&) = 0;
 
     virtual RasterPosition raster_position() const = 0;
     virtual void set_raster_position(RasterPosition const& raster_position) = 0;

Userland/Libraries/LibGPU/DeviceInfo.h

@@ -15,6 +15,7 @@ struct DeviceInfo final {
     String device_name;
     unsigned num_texture_units;
     unsigned num_lights;
+    unsigned max_clip_planes;
     u8 stencil_bits;
     bool supports_npot_textures;
 };