Replace `pypi_formula_mappings.json` with a new DSL

[p-linnane]

Verification

• This issue's title and/or description do not reference a single formula e.g. brew install wget. If they do, open an issue at https://github.com/Homebrew/homebrew-core/issues/new/choose instead.

Provide a detailed description of the proposed feature

pypi_formula_mappings.json lives in the root of Homebrew/core and is currently just over 1100 lines. Contributors are often unaware of this file and maintainers usually have to push changes to it ourselves in their PR's. It would be a lot cleaner to have this logic stored on a per-formula basis rather than referencing an external file.

What is the motivation for the feature?

Reducing complexity of formulae by having PyPI mappings within the formulae files themselves.

How will the feature be relevant to at least 90% of Homebrew users?

Contributing/maintaining Python formulae will become easier since everything is self-contained. Also reduces the instances of merge conflicts when multiple PR's change pypi_formula_mappings.json.

What alternatives to the feature have been considered?

Status quo.

[MikeMcQuaid]

Makes sense to me. Suggested DSL?

[p-linnane]

Great question. Definitely open to ideas. Just spitballing, but here's a package with all variants in the current file:

  "keyring": {
    "package_name": "keyring[completion]",
    "exclude_packages": ["cryptography"],
    "extra_packages": ["jeepney", "secretstorage"]
  },

Maybe something within a formula like:

	pypi_packages name: ["keyring[completion]"],
	pypi_packages exclude: ["pycparser"],
	pypi_packages include: ["jeepney", "secretstorage"]

[gromgit]

Seems like some redundancy can be removed:

	pypi_packages name: ["keyring[completion]"],
	              exclude: ["pycparser"],
	              include: ["jeepney", "secretstorage"]

[MikeMcQuaid]

pypi_packages name: "keyring[completion]",
              exclude: "pycparser",
              include: ["jeepney", "secretstorage"]

would be nicer still and accept String or T::Array[String].