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.
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