GAL: Fix sampler leaks on exit (#2353)

Before this, all samplers instance were leaking on exit because the
dispose method was never getting called.

This fix this issue by making TextureBindingsManager disposable and
calling the dispose method in the TextureManager.

Ryujinx.Graphics.Gpu/Image/TextureManager.cs

@@ -1286,7 +1286,7 @@ namespace Ryujinx.Graphics.Gpu.Image
         }
 
         /// <summary>
-        /// Disposes all textures in the cache.
+        /// Disposes all textures and samplers in the cache.
         /// It's an error to use the texture manager after disposal.
         /// </summary>
         public void Dispose()
@@ -1297,6 +1297,9 @@ namespace Ryujinx.Graphics.Gpu.Image
                 {
                     texture.Dispose();
                 }
+
+                _cpBindingsManager.Dispose();
+                _gpBindingsManager.Dispose();
             }
         }
     }