Clarify ExtUI command injection

Marlin/src/lcd/extensible_ui/ui_api.cpp

 
   float getFeedrate_percent() { return feedrate_percentage; }
 
-  void enqueueCommands_P(PGM_P const gcode) {
+  void injectCommands_P(PGM_P const gcode) {
     queue.inject_P(gcode);
   }
 

Marlin/src/lcd/extensible_ui/ui_api.h

   bool isMachineHomed(); // Axis position most likely correct, steppers may have deactivated
   bool canMove(const axis_t);
   bool canMove(const extruder_t);
-  void enqueueCommands_P(PGM_P const);
+  void injectCommands_P(PGM_P const);
   bool commandsInQueue();
 
   bool isHeaterIdle(const heater_t);