This simply isn’t possible. The amount of energy generated by movement is orders of magnitude lower than what a smart watches uses. You would gain, maybe, seconds of extra charge for a day. Maybe.
Edit: this also goes for the solar idea, I highly doubt it would ever happen. Even a perfectly efficient solar panel the size of the entire watch fence couldn’t get it done.
Casio hash a watch now with a solar panel on it. It isn’t a smart watch exactly but has GPS. Four hours charging in direct sunlight gets you an hour of GPS usage.
Again, what I was suggesting was nothing more than an idea and a means of keeping conversation going forward. I recognize that with today's known technologies this may be impossible to deliver or otherwise we'd maybe have a product that does this already on the market, right? Consider this, there is more computing power in our smart phones and potentially on our wrists today than the computers which powered the first rockets into space back in the 60's. If you asked scientists back in the 60's would this be possible what do you think they'd say?