[rcore][desktop_glfw] Set AUTO_ICONIFY flag to false per default

[SoloByte]

Previously AUTO_ICONIFY was only disabled if the user requested a Fullscreen window from the start. After that, changing this behavior on the user side was impossible, even when changing to a Fullscreen window.

The AUTO_ICONIFY causes problems on macOS. On macOS, if the window is minimized because of AUTO_ICONIFY then the only way to restore it is to click on the icon in the dock. In other words, when AUTO_ICONIFY is enabled alt/cmd-tabbing through Windows does not work correctly. On Windows, it works even when AUTO_ICONIFY is enabled.

Additionally, if a raylib window is in Fullscreen mode on another monitor the AUTO_ICONIFY behavior is a problem because the user might want the window to stay on the monitor even if it loses focus. (problem on all OS's)

AUTO_ICONIFY also restores the monitor hardware resolution if a fullscreen window loses focus. (is a good thing mostly but causes an issue with multiple monitors, see point above)

I set it to false per default on all operating systems to maintain consistency. The AUTO_ICONIFY behavior can be implemented by the user if needed:

void update()
{
	handleInput();

	bool currentWindowFocus = IsWindowFocused();
	if (currentWindowFocus != previousWindowFocus)
	{
		onFocusChanged(currentWindowFocus);
		previousWindowFocus = currentWindowFocus;
	}

}

void onFocusChanged(bool newFocus)
{
	if (newFocus == false) //window lost focus
	{
		if (IsWindowFullscreen())
		{
			wasFullscreen = true; //used for restoring fullscreen when window gains focus again
			ToggleFullscreen();
			MinimizeWindow();
		}
		else
		{
			if (!IsWindowMinimized()) MinimizeWindow();
		}
	}
	else // window gained focus
	{
		RestoreWindow();
		if (wasFullscreen) 
		{
			wasFullscreen = false;
			ToggleFullscreen();
		}
	}
}

---

If wanted/needed there are some other options to go about this:

1. I only set the AUTO_ICONIFY flag to false per default on macOS. (this creates problems because the behavior is different on different platforms but has the advantage that nothing changes for Windows/Linux users)
2. There is a way to set the AUTO_ICONIFY flag on the user side (like with other flags but I don't know how other backends handle this behavior)
3. AUTO_ICONIFY is set to false per default and it is only set to true whenever fullscreen mode is activated. It is set to false again once fullscreen is exited.

---

Another example that just caused me problems with the AUTO_ICONIFY flag on Windows:

I wanted to make a screenshot of a raylib window for another PR using the Snipping Tool app. With the AUTO_ICONIFY flag enabled I could not do that because every time I focused the window of the snipping tool to make a screenshot the raylib window automatically minimized... So I am really for just disabling it.

[raysan5]

@SoloByte Thanks for the review