Use celsius_t for temperature accessors

Marlin/src/gcode/bedlevel/G26.cpp

         layer_height          = MESH_TEST_LAYER_HEIGHT,
         prime_length          = PRIME_LENGTH;
 
-  int16_t bed_temp            = MESH_TEST_BED_TEMP,
-          hotend_temp         = MESH_TEST_HOTEND_TEMP;
+  celsius_t bed_temp          = MESH_TEST_BED_TEMP,
+            hotend_temp       = MESH_TEST_HOTEND_TEMP;
 
   float nozzle                = MESH_TEST_NOZZLE_SIZE,
         filament_diameter     = DEFAULT_NOMINAL_FILAMENT_DIA,

Marlin/src/module/temperature.h

     //inline so that there is no performance decrease.
     //deg=degreeCelsius
 
-    FORCE_INLINE static float degHotend(const uint8_t E_NAME) {
+    FORCE_INLINE static celsius_t degHotend(const uint8_t E_NAME) {
       return TERN0(HAS_HOTEND, temp_hotend[HOTEND_INDEX].celsius);
     }
 
       #if ENABLED(SHOW_TEMP_ADC_VALUES)
         FORCE_INLINE static int16_t rawProbeTemp()    { return temp_probe.raw; }
       #endif
-      FORCE_INLINE static float degProbe()            { return temp_probe.celsius; }
+      FORCE_INLINE static celsius_t degProbe()        { return temp_probe.celsius; }
       FORCE_INLINE static bool isProbeBelowTemp(const_float_t target_temp) { return temp_probe.celsius < target_temp; }
       FORCE_INLINE static bool isProbeAboveTemp(const_float_t target_temp) { return temp_probe.celsius > target_temp; }
       static bool wait_for_probe(const_float_t target_temp, bool no_wait_for_cooling=true);
       #if ENABLED(SHOW_TEMP_ADC_VALUES)
         FORCE_INLINE static int16_t rawChamberTemp()      { return temp_chamber.raw; }
       #endif
-      FORCE_INLINE static float degChamber()              { return temp_chamber.celsius; }
+      FORCE_INLINE static celsius_t degChamber()          { return temp_chamber.celsius; }
       #if HAS_HEATED_CHAMBER
         FORCE_INLINE static celsius_t degTargetChamber()  { return temp_chamber.target; }
         FORCE_INLINE static bool isHeatingChamber()       { return temp_chamber.target > temp_chamber.celsius; }
       #if ENABLED(SHOW_TEMP_ADC_VALUES)
         FORCE_INLINE static int16_t rawCoolerTemp()     { return temp_cooler.raw; }
       #endif
-      FORCE_INLINE static float degCooler()             { return temp_cooler.celsius; }
+      FORCE_INLINE static celsius_t degCooler()         { return temp_cooler.celsius; }
       #if HAS_COOLER
         FORCE_INLINE static celsius_t degTargetCooler() { return temp_cooler.target; }
         FORCE_INLINE static bool isLaserHeating()       { return temp_cooler.target > temp_cooler.celsius; }