[PATCH 2/3] gdiplus: Add internal string format properties used by EMF+ records

[Vincent Povirk]

I think the margins in default_drawstring_format should be 1/6. It's
not currently used in GdipDrawString or GdipMeasureString, but that's
something we may change in the future. Also, they're copied over to
generic_default_format which would've had 1/6 margins previously.