Add sources to bst shell

Background

We want to be able to run software debuggers & co when we run bst shell

Task description

• Modify bst shell to include the sources of all open workspaces in a given project
• Potentially add a flag to enable/disable the feature (undecided)

Steps

• Find the point were artifacts are added to the sandbox
• Get a list of all open workspaces
• Get the build-root for the elements of each workspace
• Recreate the full path of each workspace inside the sandbox
  • This is to allow existing debug logs and paths to find the right path
  • In the case of conflicting paths between workspaces, the shell will abort and instruct the user to close some/all of the conflicting workspaces
• Copy the contents of the workspaces into their corresponding directory
• Add tests to confirm that the files were copied into the sandbox

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