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.

EM_GETPARAFORMAT previously would overwrite the cbSize field with the
size of PARAFORMAT2, would read past the end of the struct, and might
indicate that PARAFORMAT2 fields are valid using the mask regardless
of the value of cbSize.

If a EM_SETPARAFORMAT message is sent to the richedit control with bits
in the dwMask field that correspond to PARAFORMAT2 fields, then these
fields should be ignored.  Instead data was copied from outside of the
structure.