Revert "Graphics/RenderTechnique: Remove Clear method"

This reverts commit 8aa3764660d5c98995135f736ecd710677fa240c [formerly 9b4ec3ae32492e383c19a06bd1c3e461b3fcf46d].

It seems I was wrong about the Clear method, my revert broke the Deferred Rendering


Former-commit-id: b8d2db34ffd9d24798670f19aba0de88f5b77a1c

include/Nazara/Graphics/AbstractRenderTechnique.hpp

@@ -28,6 +28,7 @@ namespace Nz
 			AbstractRenderTechnique(AbstractRenderTechnique&&) = default;
 			virtual ~AbstractRenderTechnique();
 
+			virtual void Clear(const SceneData& sceneData) const = 0;
 			virtual bool Draw(const SceneData& sceneData) const = 0;
 
 			virtual void EnableInstancing(bool instancing);