review fullscreen support

[ColleagueRiley]

• create enum RGFW_fullscreenMode for no fullscreen, exclusive fullscreen or borderless fullscreen modes and comments direclty defining what these modes mean for the user
• allow the user to set the fullscreen mode using RGFW_window_setFullscreen
• use RGFW_window_setFullscreen as a standard function in RGFW, to standardize fullscreen behavior across each platform, using RGFW_window_setFullscreenPlatform for platform specific code
• save the fullscreen monitor to avoid bugs
• save the border state so that way the window returns to the original border state rather than possibly creating a bug if the window was borderless to begin with