Modular light transformers (#2124)

esphome/components/light/light_output.h

@@ -3,6 +3,7 @@
 #include "esphome/core/component.h"
 #include "light_traits.h"
 #include "light_state.h"
+#include "light_transformer.h"
 
 namespace esphome {
 namespace light {
@@ -13,6 +14,9 @@ class LightOutput {
   /// Return the LightTraits of this LightOutput.
   virtual LightTraits get_traits() = 0;
 
+  /// Return the default transformer used for transitions.
+  virtual std::unique_ptr<LightTransformer> create_default_transition();
+
   virtual void setup_state(LightState *state) {}
 
   virtual void write_state(LightState *state) = 0;