BTEmu: Add helper function for accessing WiimoteDevice instances by index

This makes it much more straightforward to access WiimoteDevice
instances and also keeps the implementation details of accessing those
instances in one spot.

Given as all external accesses to the WiimoteDevice instances go through
this function, we can make the other two private.

Source/Core/DolphinQt2/MainWindow.cpp

@@ -1401,7 +1401,7 @@ void MainWindow::OnConnectWiiRemote(int id)
   Core::RunAsCPUThread([&] {
     const auto bt = std::static_pointer_cast<IOS::HLE::Device::BluetoothEmu>(
         ios->GetDeviceByName("/dev/usb/oh1/57e/305"));
-    const bool is_connected = bt && bt->AccessWiiMote(id | 0x100)->IsConnected();
+    const bool is_connected = bt && bt->AccessWiiMoteByIndex(id)->IsConnected();
     Wiimote::Connect(id, !is_connected);
   });
 }

Source/Core/DolphinQt2/MenuBar.cpp

@@ -914,14 +914,16 @@ void MenuBar::UpdateToolsMenu(bool emulation_started)
   const auto bt = ios ? std::static_pointer_cast<IOS::HLE::Device::BluetoothEmu>(
                             ios->GetDeviceByName("/dev/usb/oh1/57e/305")) :
                         nullptr;
-  bool enable_wiimotes =
+  const bool enable_wiimotes =
       emulation_started && bt && !SConfig::GetInstance().m_bt_passthrough_enabled;
 
-  for (int i = 0; i < 5; i++)
+  for (std::size_t i = 0; i < m_wii_remotes.size(); i++)
   {
-    m_wii_remotes[i]->setEnabled(enable_wiimotes);
+    QAction* const wii_remote = m_wii_remotes[i];
+
+    wii_remote->setEnabled(enable_wiimotes);
     if (enable_wiimotes)
-      m_wii_remotes[i]->setChecked(bt->AccessWiiMote(0x0100 + i)->IsConnected());
+      wii_remote->setChecked(bt->AccessWiiMoteByIndex(i)->IsConnected());
   }
 }