Scaffold / Basic Dev Environment

[gnumonik]

Description of the change

DO NOT MERGE THIS - PRIMITIVE SCAFFOLD/DEV ENVIRONMENT SETUP

This PR does a few things that should enable a basic development environment and provide a sandbox for experimentation:

• Modifies cabal.project to provide plutus-core via CHaP
• Adds a shell.nix which supplies system libraries, GHC, HLS, Cabal (required to build the project)
• Adds a uplc codegen target option to purs compile. E.g. purs compile -g uplc
• Adds a placeholder Laguage.PureScript.CodeGen.UPLC module & placeholder moduleToUPLC function
• Slightly modifies the build pipeline to invoke moduleToUPLC and print the result to the console

The idea is that someone who wants to play around can fill in the moduleToUPLC function in Language.PureScript.CodeGen.UPLC and inspect the results. Eventually we'll want better scaffolding, but this is enough to start playing around.

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Checklist:

• Added a file to CHANGELOG.d for this PR (see CHANGELOG.d/README.md)
• Added myself to CONTRIBUTORS.md (if this is my first contribution)
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation
• Added a test for the contribution (if applicable)