Enforces the time unit being returned and also allows using the standard
time utilities to manipulate it.

C++17 adds clamp() to the standard library, so we can remove ours in
favor of it.

Adds in a missing EndGameFrame when nvdrv swaps buffers

Now based on std::chrono, and also works in terms of emulated time
instead of frames, so we can in the future frame-limit even when the
display is disabled, etc.

The frame limiter can also be enabled along with v-sync now, which
should be useful for those with displays running at more than 60 Hz.

More ergonomic to use and will be required for upcoming changes.