Copy benckmark deps into directory (#5159)
### Description
#5156 turned out to be flakey, and it seems our root detection will
prevent us from running the local `next` package unless we copy it over
into the benchmark app.
I _really_ hate our root detection, and think we should get rid of it. I
don't care where the file is located, it should be readable by our
bundler.
### Testing Instructions
