Possbility of storing data in D3D9 objects via GetPrivateData/SetPrivateData

[AlpyneDreams]

This may be useful in cases where we'd rather not cache stuff such as pointers to D3D8 objects.

To do this, would want to add an optimized fast path case for certain (or all) uses of Set/GetPrivateData (current ComPrivateData implementation is O(n)) in D3D9. Note that there would probably still be more overhead than caching but less validation issues I imagine. Caching does work fine for the time being.