GDK-Win32: Use SetProcessDpiAwarenessContext() where available

GDK-Win32: Use SetProcessDpiAwarenessContext() where available

This allows us to use DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2 for the
DPI awareness mode, which will help us to better support use cases with
multiple monitors.  This is actualy a more advaned version of the
current PROCESS_PER_MONITOR_DPI_AWARE via using SetProcessDpiAwareness().

Note that this is not enabled by default, but also enabled via using
GDK_WIN32_PER_MONITOR_HIDPI, as in the PROCESS_PER_MONITOR_DPI_AWARE
case.

Note also, that appliation compatibility settings and DPI-awareness
manifests takes precedence over this API call, as before.