comdlg32: We need to be able to type the decimal separator into the margin edit controls so ES_NUMBER is no use. Subclass them and filter WM_CHAR instead.

comdlg32: Set the margins groupbox title to reflect whether we are using metric or imperial measurements.

Other than being a bit nicer than passing function pointers all over the
place, this helps dxgi/d3d10. While the swapchain itself is created in dxgi,
its surfaces are constructed in d3d10core, which makes it impractical for dxgi
to pass the appropriate function pointers.