GDK W32: Correctly infer gtk-xft-antialias & gtk-xft-rgba

LRN requested to merge lrn/gtk:gtk-3-24-w32-xsettings-defaults into gtk-3-24

Instead of hardcoding gtk-xft-antialias, use SPI_GETFONTSMOOTHING to determine whether antialiasing is enabled.

Make gtk-xft-rgba query more complex - try to determine display orientation, then use that to rotate subpixel structure. This won't help with monitors that have naturally vertical subpixels, but should improve things for monitors that are rotated (as long as Windows display settings are adjusted accordingly).

Partially fixes #1774 (closed)

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