GDK W32: Use PROCESS_PER_MONITOR_DPI_AWARE
According to Microsoft documentation, PROCESS_SYSTEM_DPI_AWARE, just as PROCESS_DPI_UNAWARE, allows Windows to scale GTK windows and do all kinds of stuff. To ensure this doesn't happen, we need to use PROCESS_PER_MONITOR_DPI_AWARE, even if GTK does not really handle DPI changes dynamically via the WM_DPICHANGED message.
This completely prevents Windows from scaling GTK windows when they are moved between screens with different scaling set up.
Fixes #3734