render/pass: add wlr_render_texture_options.transfer_function

Also add a bit in wlr_renderer.features to indicate support.

include/wlr/render/wlr_renderer.h

@@ -41,6 +41,10 @@ struct wlr_renderer {
 	} events;
 
 	struct {
+		/**
+		 * Whether color transforms are supported for input textures
+		 */
+		bool input_color_transform;
 		/**
 		 * Does the renderer support color transforms on its output?
 		 */