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.Common/Configuration/ConfigurationFileFormat.cs

@@ -14,7 +14,7 @@ namespace Ryujinx.Configuration
         /// <summary>
         /// The current version of the file format
         /// </summary>
-        public const int CurrentVersion = 24;
+        public const int CurrentVersion = 25;
 
         public int Version { get; set; }