Add custom refresh rate mode to VSync option (#238)

Rebased @jcm93's refreshinterval branch:
https://github.com/jcm93/Ryujinx/tree/refreshinterval

The option is placed under System/Hacks. Disabled, it's the default
Ryujinx behavior. Enabled, the behavior is shown in the attached
screenshots. If a framerate is too high or low, you can adjust the value
where you normally toggle VSync on and off. It will also cycle through
the default on/off toggles.

Also, in order to reduce clutter, I made an adjustment to remove the
target FPS and only show the percentage.

---------

Co-authored-by: jcm <6864788+jcm93@users.noreply.github.com>

src/Ryujinx.Graphics.GAL/Multithreading/ThreadedWindow.cs

@@ -31,7 +31,7 @@ namespace Ryujinx.Graphics.GAL.Multithreading
             _impl.Window.SetSize(width, height);
         }
 
-        public void ChangeVSyncMode(bool vsyncEnabled) { }
+        public void ChangeVSyncMode(VSyncMode vSyncMode) { }
 
         public void SetAntiAliasing(AntiAliasing effect) { }