Add unmaximize() to WindowManager

[Eoin-k]

If a window is maximized and you try to resize it, this was being ignored by the window.
The only workaround I was able to find was by calling Window::minimize() then Window::open() before resizing, which worked but looked strange having the window close and reopen in a different place and size.

Example - original resize and position as a sidebar:
Window::minimize();
Window::open();
Window::resize($width, $screenHeight, 'main');
Window::position(0, 0, true, 'main');

Now with the Window::unmaximize() the window just drops out of maximized state to whatever the previous dimensions were and the resize or any window function can be called directly after.

Once the electron plugin is rebuilt with these changes it works as expected and also emits the WindowUnmaximized event.

[gwleuverink]

Thanks for your contribution! 🙏🏻

[gwleuverink]

The checks fail because they run outside the org. Both Pint & plugin build run fine locally. Ok to merge!