Purpose

This PR adds infrastructure for selectable Python engines in the Python Script and Python Script From String nodes, and in addition to the original IronPython 2.7 engine, also supports a CPython 3.7 evaluation engine via Python.NET.

Engines are selectable via anew Engine string property on the node, but there is no UI for this property yet, it can only be specified in the .dyn file.

Todo before merge:

• Restore autocompletion (currently disabled)
• Restrict IronPython & Python.NET nuget dependencies to evaluator DLLs
• API comments

Declarations

Check these if you believe they are true

• The codebase is in a better state after this PR
• Is documented according to the standards
• The level of testing this PR includes is appropriate
• User facing strings, if any, are extracted into *.resx files
• All tests pass using the self-service CI.
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning and are documented in the API Changes document.

API Changes

• New property PythonNodeBase.Engine
• New assembly DSCPython