Fixed back button problems in UWP

[timgott]

The back button on Windows 10 Mobile was not always reliable because GamePad.Back could be changed by the UI thread during a tick. Sometimes the button would do nothing because the game checked GamePadState before GamePad.Back was changed, which was reset to false in the end of the tick.

[nkast]

It sounds right to me.

@atomgott ,
While you are at it, is it possible to move the code inside UAPGameWindow.ProcessWindowEvents() ?

MonoGame/MonoGame.Framework/WindowsUniversal/UAPGameWindow.cs

Lines 340 to 364 in 589bcf4

	void ProcessWindowEvents()
	{
	// Update input
	_inputEvents.UpdateState();
	// Update TextInput
	if(!_textQueue.IsEmpty)
	UpdateTextInput();
	// Update size
	if (_isSizeChanged)
	UpdateSize();
	// Update orientation
	if (_isOrientationChanged)
	UpdateOrientation();
	if (_isFocusChanged)
	UpdateFocus();
	}
	internal void Tick()
	{
	// Update state based on window events.
	ProcessWindowEvents();

This way we will have all Event Sync code nice and tide in one place.

[Jjagg]

@atomgott Don't worry about the build failure, it's not because of this PR :)

[timgott]

Oh ok :)
I'm sorry about all the whitespace changes, I think that was Visual Studio trying to help

[Jjagg]

You can see the diff without the whitespace changes by adding ?w=1 to the URL like so: https://github.com/MonoGame/MonoGame/pull/5810/files?w=1

[nkast]

Great job @atomgott

I just have to say that there's still a race condition although a very slim possibility of occurring.
thread#0 L314: GamePad.Back = _backPressed;
thread#1 L307: _backPressed = true;
thread#0 L315: _backPressed = false;
edit: It would be tricky to resolve this without expensive locking or whatever. Anyways, this is definitely a major improvement from before.