Add option to start window maximized

[jf908]

What problem does this solve or what need does it fill?

There is currently no functionality to start bevy with a maximized window. Ideally a window should remember its state between relaunches, including whether its maximized.

What solution would you like?

While you can technically use window.set_maximized(true) before Bevy launches, this creates a window which maximized on the next tick which looks janky. Instead it should just create the window maximized.