Updates our build script to pull down the artifacts like we do in CI for
building v8 into our targets.
This changes the flow so that we now pre-install rusty v8 assets for all
of our release targets from pre-built in workflow.
Secondarily if running it locally we now optionally pull the assets down
on python run assuming the user hasn't set the proper values, it then
provides them.
Sorry for the miss here.
Channing Conger