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/sdl/sdl.h

@@ -4,8 +4,21 @@
 
 #pragma once
 
+#include <memory>
+#include <vector>
 #include "core/frontend/input.h"
 
+union SDL_Event;
+namespace Common {
+class ParamPackage;
+}
+namespace InputCommon {
+namespace Polling {
+class DevicePoller;
+enum class DeviceType;
+} // namespace Polling
+} // namespace InputCommon
+
 namespace InputCommon {
 namespace SDL {
 
@@ -15,5 +28,15 @@ void Init();
 /// Unresisters SDL device factories and shut them down.
 void Shutdown();
 
+/// Creates a ParamPackage from an SDL_Event that can directly be used to create a ButtonDevice
+Common::ParamPackage SDLEventToButtonParamPackage(const SDL_Event& event);
+
+namespace Polling {
+
+/// Get all DevicePoller that use the SDL backend for a specific device type
+std::vector<std::unique_ptr<InputCommon::Polling::DevicePoller>> GetPollers(
+    InputCommon::Polling::DeviceType type);
+
+} // namespace Polling
 } // namespace SDL
 } // namespace InputCommon