Expose lambda action to reset a cycle in slow_pwm (#4158)

esphome/components/slow_pwm/slow_pwm_output.cpp

@@ -70,7 +70,7 @@ void SlowPWMOutput::dump_config() {
 void SlowPWMOutput::write_state(float state) {
   this->state_ = state;
   if (this->restart_cycle_on_state_change_)
-    this->period_start_time_ = millis();
+    this->restart_cycle();
 }
 
 }  // namespace slow_pwm

esphome/components/slow_pwm/slow_pwm_output.h

@@ -14,6 +14,7 @@ class SlowPWMOutput : public output::FloatOutput, public Component {
   void set_restart_cycle_on_state_change(bool restart_cycle_on_state_change) {
     restart_cycle_on_state_change_ = restart_cycle_on_state_change;
   }
+  void restart_cycle() { this->period_start_time_ = millis(); }
 
   /// Initialize pin
   void setup() override;