ControllerInterface: Add RemoveDevice()

This adds RemoveDevice() to ControllerInterface, fixes ExpressionParser
and some other code to support device removals without crashing,
and adds an IsValid() method to Device, to prepare for hotplugging.

Source/Core/InputCommon/ControllerInterface/ControllerInterface.cpp

@@ -160,6 +160,14 @@ void ControllerInterface::AddDevice(std::shared_ptr<ciface::Core::Device> device
   m_devices.emplace_back(std::move(device));
 }
 
+void ControllerInterface::RemoveDevice(std::function<bool(const ciface::Core::Device*)> callback)
+{
+  std::lock_guard<std::mutex> lk(m_devices_mutex);
+  m_devices.erase(std::remove_if(m_devices.begin(), m_devices.end(),
+                                 [&callback](const auto& dev) { return callback(dev.get()); }),
+                  m_devices.end());
+}
+
 //
 // UpdateInput
 //