Add ExtUI Flow Rate method (#16048)

Marlin/src/lcd/extensible_ui/ui_api.cpp

@@ -683,12 +683,17 @@ namespace ExtUI {
   #endif
 
   feedRate_t getFeedrate_mm_s()                       { return feedrate_mm_s; }
+  int16_t getFlowPercentage(const extruder_t extr)    { return planner.flow_percentage[extr]; }
   feedRate_t getMinFeedrate_mm_s()                    { return planner.settings.min_feedrate_mm_s; }
   feedRate_t getMinTravelFeedrate_mm_s()              { return planner.settings.min_travel_feedrate_mm_s; }
   float getPrintingAcceleration_mm_s2()               { return planner.settings.acceleration; }
   float getRetractAcceleration_mm_s2()                { return planner.settings.retract_acceleration; }
   float getTravelAcceleration_mm_s2()                 { return planner.settings.travel_acceleration; }
   void setFeedrate_mm_s(const feedRate_t fr)          { feedrate_mm_s = fr; }
+  void setFlow_percent(const int16_t flow, const extruder_t extr) {
+    planner.flow_percentage[extr] = flow;
+    planner.refresh_e_factor(extr);
+  }
   void setMinFeedrate_mm_s(const feedRate_t fr)       { planner.settings.min_feedrate_mm_s = fr; }
   void setMinTravelFeedrate_mm_s(const feedRate_t fr) { planner.settings.min_travel_feedrate_mm_s = fr; }
   void setPrintingAcceleration_mm_s2(const float acc) { planner.settings.acceleration = acc; }

Marlin/src/lcd/extensible_ui/ui_api.h

@@ -126,6 +126,7 @@ namespace ExtUI {
   float getRetractAcceleration_mm_s2();
   float getTravelAcceleration_mm_s2();
   float getFeedrate_percent();
+  int16_t getFlowPercentage(const extruder_t);
   uint8_t getProgress_percent();
   uint32_t getProgress_seconds_elapsed();
 
@@ -172,6 +173,7 @@ namespace ExtUI {
   void setRetractAcceleration_mm_s2(const float);
   void setTravelAcceleration_mm_s2(const float);
   void setFeedrate_percent(const float);
+  void setFlow_percent(const int16_t, const extruder_t);
   void setUserConfirmed();
 
   #if ENABLED(LIN_ADVANCE)