Add wrappers to invalidate buffer data & texture images

[j-o]

Problem: glInvalidateBuffer[Sub]Data functions require direct state access and don't have equivalents in the legacy implementation; the current solution simply logs a critical error message then. How would you handle this?

[scheibel]

The changes seems fine. Do you have already tested the implementations?

I'm not sure how to uniformly handle the missing OpenGL functions for fallback implementations, but for now, your solution suffices.