This function is ready to be moved into linalg. We will make torch.tensordot an alias. The only thing that needs doing is to update the documentation in line with the rest of the docs of torch.linalg.

cc @jianyuh @nikitaved @pearu @mruberry @heitorschueroff @walterddr @IvanYashchuk @xwang233 @lezcano @rgommers @pmeier @asmeurer @leofang @AnirudhDagar @asi1024 @emcastillo @kmaehashi