Add methods to grab the depth/stencil buffers too

Could probably use help here, I'm not sure if I'm doing it wrong or it's just that the games I tested had no values here (I seemed to just be getting 0s.)

The idea is there might be some toggle to show stencil / depth for the framebuffer preview.  That would make it easier to check depth write issues, etc., I think.

It can be tested by changing this line:

```
	case PAUSE_GETFRAMEBUF:
		bufferResult = gpuDebug->GetCurrentFramebuffer(bufferFrame);
		break;
```

To `GetCurrentDepthbuffer()` or etc.

-[Unknown]