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.h

@@ -4,7 +4,13 @@
 
 #pragma once
 
+#include <memory>
 #include <string>
+#include <vector>
+
+namespace Common {
+class ParamPackage;
+}
 
 namespace InputCommon {
 
@@ -31,4 +37,30 @@ std::string GenerateKeyboardParam(int key_code);
 std::string GenerateAnalogParamFromKeys(int key_up, int key_down, int key_left, int key_right,
                                         int key_modifier, float modifier_scale);
 
+namespace Polling {
+
+enum class DeviceType { Button, Analog };
+
+/**
+ * A class that can be used to get inputs from an input device like controllers without having to
+ * poll the device's status yourself
+ */
+class DevicePoller {
+public:
+    virtual ~DevicePoller() = default;
+    /// Setup and start polling for inputs, should be called before GetNextInput
+    virtual void Start() = 0;
+    /// Stop polling
+    virtual void Stop() = 0;
+    /**
+     * Every call to this function returns the next input recorded since calling Start
+     * @return A ParamPackage of the recorded input, which can be used to create an InputDevice.
+     *         If there has been no input, the package is empty
+     */
+    virtual Common::ParamPackage GetNextInput() = 0;
+};
+
+// Get all DevicePoller from all backends for a specific device type
+std::vector<std::unique_ptr<DevicePoller>> GetPollers(DeviceType type);
+} // namespace Polling
 } // namespace InputCommon