ExtUI event for PID tuning start (#21734)

Marlin/src/lcd/extui/ui_api.h

@@ -57,7 +57,7 @@ namespace ExtUI {
   enum extruder_t : uint8_t { E0, E1, E2, E3, E4, E5, E6, E7 };
   enum heater_t   : uint8_t { H0, H1, H2, H3, H4, H5, BED, CHAMBER, COOLER };
   enum fan_t      : uint8_t { FAN0, FAN1, FAN2, FAN3, FAN4, FAN5, FAN6, FAN7 };
-  enum result_t   : uint8_t { PID_BAD_EXTRUDER_NUM, PID_TEMP_TOO_HIGH, PID_TUNING_TIMEOUT, PID_DONE };
+  enum result_t   : uint8_t { PID_STARTED, PID_BAD_EXTRUDER_NUM, PID_TEMP_TOO_HIGH, PID_TUNING_TIMEOUT, PID_DONE };
 
   constexpr uint8_t extruderCount = EXTRUDERS;
   constexpr uint8_t hotendCount   = HOTENDS;

Marlin/src/module/temperature.cpp

@@ -551,6 +551,8 @@ volatile bool Temperature::raw_temps_ready = false;
 
     TERN_(HAS_AUTO_FAN, next_auto_fan_check_ms = next_temp_ms + 2500UL);
 
+    TERN_(EXTENSIBLE_UI, ExtUI::onPidTuning(ExtUI::result_t::PID_STARTED));
+
     if (target > GHV(CHAMBER_MAX_TARGET, BED_MAX_TARGET, temp_range[heater_id].maxtemp - (HOTEND_OVERSHOOT))) {
       SERIAL_ECHOLNPGM(STR_PID_TEMP_TOO_HIGH);
       TERN_(EXTENSIBLE_UI, ExtUI::onPidTuning(ExtUI::result_t::PID_TEMP_TOO_HIGH));