These options allow the files output when using `--scie {eager,lazy}`
scies to be better controlled. The `--scie-only` option provides a way
to ensure no PEX file is output, just the resulting scie. The
`--scie-name-style` option allows control over how the scie's target
platform is incorporated in the scie file name.

These are likely better than the Pex PEX for most Pex binary use cases
since they include the management extra and run in `--venv` mode as well
as providing BusyBox support for equal footing of the `pex`, `pex-tools`
and `pex3` top-level commands.

Add a `--scie-busybox-pex-entrypoint-env-passthrough` option to trade a
small amount of perf for a Pex scie busybox accepting
PEX_{INTERPRETER,MODULE,SCRIPT} entry point control like its Pex PEX
sibling.

…e/pex-scies