API: OpenGL - Full screen windows

[bryphe]

Currently, we only support 'maximized' windows. However, it's desirable to have a full-screen experience.

In GLFW, this is described in the window guide and can be set with the glfwSetWindowMonitor API. Fullscreen mode can be unset with this same API.

On the web, we can use Element.requestFulllscreen and Document.exitFullScreen to enter / exit fullscreen mode. https://developer.mozilla.org/en-US/docs/Web/API/Fullscreen_API.

My proposal is to implement the glfwSetWindowMonitor API, and use the Element.requestFullScreen/Document.exitFullscreen depending on whether the monitor parameter is set/unset.

To test this - we can add a key handler for f key, which toggles fullscreen mode in the sample app.