Support `--deps all` in `artifact checkout`

James Ennisrequested to merge
jennis/add_deps_all_to_checkout into master

Description

As it currently stands bst source checkout supports --deps all, yet bst artifact checkout does not. We should try to be consistent.

!1590 (merged) is a step towards making source checkout more like artifact checkout, however, we've agreed that artifact checkout should probably support --deps all.

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