Enhancement: Add an option to toggle VSync at runtime, and add an option for adaptive VSync

[EliteMasterEric]

Currently, VSync is enabled/disable via a window flag, and can currently only be set via a flag in the project settings.

However, from what I've read, there should be no issue with adding a function to allow the application to change the VSync mode.

This would require making this call into its own function, then making that accessible on the Window object (either via a function or a property variable).

lime/project/src/backend/sdl/SDLWindow.cpp

Lines 222 to 230 in 99ca58d

	if (flags & WINDOW_FLAG_VSYNC) {
	SDL_GL_SetSwapInterval (1);
	} else {
	SDL_GL_SetSwapInterval (0);
	}

Adding this feature would enable applications to provide a configuration option for users to enable or disable VSync.

Additionally, while we're at it, we should also add the option to use Adaptive VSync. This is done by passing -1 to the swap interval function, and returns an error if it is not supported (see the SDL documentation). In this case, the option should probably be an enumeration rather than a boolean value.

[ACrazyTown]

There's an open pull request for toggleable vsync: #1698

[dimensionscape]

Iirc, this caused random crashes on older versions of SDL, and required recreating the window. I do believe that it is fixed in current versions though, so let me give it some testing and see what comes of it.