[4/6] d3dx9: Implement ID3DXFont_GetDC [resent]

[Tony Wasserka]

- glyphs will be "drawn" in GetGlyphData using GetGlyphOutline (with
GGO_GRAY8_BITMAP), so we don't need to select a bitmap into the DC.
- the DC must be kept during the whole lifetime of the ID3DXFont object,
as 1) the pointer returned by GetDC is always the same and 2) we'll need
the DC whenever calling GetGlyphData (which is for every glyph drawn
using DrawText), so creating one on demand is not a real option.
- Using the DC of the (not yet existant) buffer texture is not an
option, as IDirect3DTexture9_GetDC is said to not work well with alpha
channels.