Add compile flag for replacing Dataform core in project directory

[mattkocak]

Add a flag for the compile CLI command that replaces @dataform/core in the project directory with a build based on code present in the current directory. This flag helps developers test code changes to Dataform core. Resolves #1629.

Example use of this flag: ./scripts/run compile my_project --replace-core

Hey @BenBirt, this is an implementation for the older issue linked above that we had briefly corresponded on. I'd be happy to make any additions or changes as the team sees fit.

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