fix(pypi): pass requirements without env markers to the whl_library (#2488)

With this change the environment markers from the requirements.txt files
no longer end up in the whl_library definitions. I am reusing a function
that already is parsing each requirement line for `sha256` values and
added
logic to extract the `marker` at that point. This means that the change
is
also trivial to backport to the `WORKSPACE` and the logic in the
extension
becomes simpler and we don't rely only on integration tests.

Expected changes to the users:
* If they have vendored pip requirements in `WORKSPACE`, those will be
  reformatted and the env markers will be removed.
* The `MODULE.bazel.lock` file will be likewise reformatted if users are
not using `--experimental_index_url`. Also, the env markers will not be
  passed in the `requirement`.
* `bazel query 'deps("@pypi//foo")'` should start working in more cases.

Fixes #2450.

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Co-authored-by: Richard Levasseur <richardlev@gmail.com>