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.Headless.SDL2/Program.cs

@@ -563,7 +563,7 @@ namespace Ryujinx.Headless.SDL2
                 window,
                 options.SystemLanguage,
                 options.SystemRegion,
-                !options.DisableVSync,
+                options.VSyncMode,
                 !options.DisableDockedMode,
                 !options.DisablePTC,
                 options.EnableInternetAccess,
@@ -580,7 +580,8 @@ namespace Ryujinx.Headless.SDL2
                 Common.Configuration.Multiplayer.MultiplayerMode.Disabled,
                 false,
                 "",
-                "");
+                "",
+                options.CustomVSyncInterval);
 
             return new Switch(configuration);
         }