implement `--pack` using the sbpack code in `cwl-utils`

[mr-c]

https://github.com/common-workflow-language/cwl-utils/blob/main/cwl_utils/pack.py

• enhance tests to confirm that this fixes all issues listed in Meta: list of bugs incwltool --pack #1611 and cwltool --pack does not handle collisions correctly #1937