[Windows] Window positions across monitors with different scale factors #63

On Windows, Window::GetPosition() / SetPosition() (and the bounds calls) convert between logical and physical pixels with the scale factor of the monitor the window is currently on (GetScaleFactorForWindow). With monitors at different scale factors, the same logical point maps to different physical points depending on where the window is. Saving a position on one monitor and restoring it (or restoring on another monitor) puts the window in the wrong place or makes it the wrong size.

Expected: one global coordinate space that matches DisplayManager's display bounds. That means converting with the scale factor of the monitor that contains the target point, and handling the WM_DPICHANGED resize that follows a move across monitors.

Background:

• getPosition and setPosition don't work correctly on Windows with multiple scaled screens leanflutter/window_manager#474: getPosition/setPosition wrong with multiple scaled screens (also #448, #536, #589)