fix(windows): decoupling the effects of switching between fullscreen and maximized.

[owtotwo]

Problem

As mentioned here

Detials

set_maximized(false) will fire the SW_RESTORE, and it disturbs the state of the borderless fullscreen.
To be precise, the window size that should have kept the full screen has been changed (to normal window size).

Solution

1. Use SetWindowLongW(... !WS_MAXIMIZE ...) instead of ShowWindow(..., SW_RESTORE) to set the maximized state off.
2. Use placement.showCmd to make it correct for set_fullscreen(false) when the window is maximized or not.