Implement global and per instance shader uniforms.

Adds two keywords to shader language for uniforms:
-'global'
-'instance'

This allows them to reference values outside the material.

servers/rendering/rendering_device.h

@@ -1025,7 +1025,6 @@ public:
 	virtual uint32_t get_frame_delay() const = 0;
 
 	static RenderingDevice *get_singleton();
-
 	RenderingDevice();
 };