Add LEVELING_DATA as a capability

Marlin/Marlin_main.cpp

       SERIAL_PROTOCOLLNPGM("Cap:Z_PROBE:0");
     #endif
 
+    // MESH_REPORT (M420 V)
+    #if PLANNER_LEVELING
+      SERIAL_PROTOCOLLNPGM("Cap:LEVELING_DATA:1");
+    #else
+      SERIAL_PROTOCOLLNPGM("Cap:LEVELING_DATA:0");
+    #endif
+
     // SOFTWARE_POWER (G30)
     #if HAS_POWER_SWITCH
       SERIAL_PROTOCOLLNPGM("Cap:SOFTWARE_POWER:1");