Make disabling SynchronizeWithVerticalRetrace work on WindowsGL

So you can disable VSync and get lots of screen tearing if that is your thing.
This is now implemented properly like it is on other platforms.

I have a little test project for this here:
https://github.com/danzel/WrapTest/compare/disable-vsync
You can move ```graphics.SynchronizeWithVerticalRetrace``` around and check the behaviour.

This is how it works in XNA (And MonoGameDX), but worked differently in WindowsGL:

Set it in Game constructor - Setting is applied. (Didn't work in GL)
Set in Initialize (No ApplyChanges) - Nothing happens (This would previously set it in GL)
Set in Initialize and ApplyChanges - Setting is applied

Fixes #1862