Implement G42, after all

Marlin/src/gcode/gcode.cpp

@@ -364,6 +364,10 @@ void GcodeSuite::process_parsed_command(const bool no_ok/*=false*/) {
           break;
       #endif
 
+      #if HAS_MESH
+        case 42: G42(); break;                                    // G42: Coordinated move to a mesh point
+      #endif
+
       #if ENABLED(CNC_COORDINATE_SYSTEMS)
         case 53: G53(); break;                                    // G53: (prefix) Apply native workspace
         case 54: G54(); break;                                    // G54: Switch to Workspace 1