WinRT: Oblique fonts aren't properly rendered when using DirectWrite loader

Fonts with "oblique" style are rendered in the normal face (bold, italic work though). Adding the style string to registerFont() doesn't seem to help (it causes fewer "duplicate" fonts to be released, but doesn't solve the problem).

It may be a bug in how we load/register fonts, or what data we get from DirectWrite, or how FreeType interprets the data. It may be that the proper solution is to get the glyph data directly from DirectWrite, rather than using the FreeType font engine.