fix(whl_library): fix the dependency generation for multi-python depenency closures

[aignas]

We start using the recently introduced is_python_config_setting to make it possible to have a working select statement when multiple python version selection needs to happen in a whl_library.

This adds further fixes so that the correct dependencies are pulled in when the python_version string flag is unset thus making this implementation suitable for bzlmod use case where we would use a single whl_library instance for multiple python versions within the hub.

Work towards #735.