[wpilib] Add robot callback that is called when the DS is initially connected (#5231)

wpilibc/src/main/native/cpp/IterativeRobotBase.cpp

@@ -24,6 +24,8 @@ IterativeRobotBase::IterativeRobotBase(units::second_t period)
 
 void IterativeRobotBase::RobotInit() {}
 
+void IterativeRobotBase::DriverStationConnected() {}
+
 void IterativeRobotBase::SimulationInit() {}
 
 void IterativeRobotBase::DisabledInit() {}
@@ -127,6 +129,11 @@ void IterativeRobotBase::LoopFunc() {
     mode = Mode::kTest;
   }
 
+  if (!m_calledDsConnected && word.IsDSAttached()) {
+    m_calledDsConnected = true;
+    DriverStationConnected();
+  }
+
   // If mode changed, call mode exit and entry functions
   if (m_lastMode != mode) {
     // Call last mode's exit function