audio: Implement a SDL2 backend (#2258)

* audio: Implement a SDL2 backend

This adds support to SDL2 as an audio backend.
It has the same compatibility level as OpenAL without its issues.

I also took the liberty of restructuring the SDL2 code to have one
shared project between audio and input.

The configuration version was also incremented.

* Address gdkchan's comments

* Fix update logic

* Add an heuristic to pick the correct target sample count wanted by the game

* Address gdkchan's comments

* Address Ac_k's comments

* Fix audren output

* Address gdkchan's comments

Ryujinx.Input.SDL2/SDL2GamepadDriver.cs

@@ -1,4 +1,5 @@
-using System;
+using Ryujinx.SDL2.Common;
+using System;
 using System.Collections.Generic;
 using static SDL2.SDL;