utils/ast: cleanup

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This is the first round of improvements for the recently-added AST helper functions

• Move add_bottle_stanza! from Utils::Bottles to Utils::AST
• Add replace_bottle_stanza!
  • I have not added tests for this function, but the existing dev-cmd/bottle tests verify that this is working
• Simplify parameters

@iMichka I know you've been working on the new cellar syntax; please feel free to open a PR and not let this PR be blocking

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Review period will end on 2020-12-30 at 11:53:02 UTC.

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Review period ended.