Setup fewer wheel repos in pip.parse

Currently we create one repository per python version per wheel repo in any hub that is configured with `experimental_index_url`.

If `pipstar` is enabled by default, we can instead just create a single repository.

TODO:
- [ ] Create a single repo for a wheel file when `pipstar` and `index_url` is used no matter how many python versions are used.
- [X] Extract the wheel using `download_and_extract` (probably depends on the venv code to be stabilized).
- [X] Parse the `entry_points.txt` in starlark

Won't do:
- Have a default interpreter that we use to extract wheels if `pipstar` is enabled.
- create `py_console_script_binary` targets and have everything backwards compatible.

This is just a laundry list of things related, so in the future I may split the ticket further. Just wanted to dump my brain a little and transfer some paper notes to the ticket tracker.