[wpilib] Add EventLoop (#4104)

This is a generic expansion of the command-based Trigger framework.

wpilibc/src/main/native/cpp/event/EventLoop.cpp

@@ -0,0 +1,30 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "frc/event/EventLoop.h"
+
+using namespace frc;
+
+EventLoop::EventLoop() {}
+
+void EventLoop::Binding::Poll() {
+  if (condition()) {
+    action();
+  }
+}
+
+void EventLoop::Bind(std::function<bool()> condition,
+                     wpi::unique_function<void()> action) {
+  m_bindings.emplace_back(Binding{condition, std::move(action)});
+}
+
+void EventLoop::Poll() {
+  for (Binding& binding : m_bindings) {
+    binding.Poll();
+  }
+}
+
+void EventLoop::Clear() {
+  m_bindings.clear();
+}