Allow input configuration with SDL joysticks (#3116)

* Add infrastructure to poll joystick input and get ParamPackages

* Generalize the callbacks in configure_input.cpp and add buttons for analog sticks

* Use the polling classes in the input dialog

* Fix includes

* Formatting fix

* Include real header instead of forward declaring, to fix compiler error

* Split up pair and add deadzone for joystick configuration

* Pass ParamPackages by reference to callback

* fix formatting

* getPollers -> GetPollers

* Add forward declarations and simplify code a bit

* Update joysticks before opening them

* Fix mixup between joystick IDs and device indices

src/input_common/main.cpp

@@ -71,4 +71,15 @@ std::string GenerateAnalogParamFromKeys(int key_up, int key_down, int key_left,
     return circle_pad_param.Serialize();
 }
 
+namespace Polling {
+
+std::vector<std::unique_ptr<DevicePoller>> GetPollers(DeviceType type) {
+#ifdef HAVE_SDL2
+    return SDL::Polling::GetPollers(type);
+#else
+    return {};
+#endif
+}
+
+} // namespace Polling
 } // namespace InputCommon