D3D: Add geometry shader stereoscopy support.

Continuation of PR #1439. Like the OGL backend MSAA and XFB are not yet supported.

Besides the usual stereoscopy modes the D3D also offers support for Nvidia 3D Vision. Allowing you to use the native stereoscopy with the 3D Vision platform.

### To-do
- [x] Add anaglyph shader support.
- [ ] Enable stereoscopy options.
Maybe just add a comment saying where the struct is from for the time being.