Reduce standalone build size

[JLHwung]

Q	A
License	MIT

In this PR we build babel-standalone against the src version of @babel/* dependencies instead of lib, which is specified in their package.json. By doing so the transform-runtime can replace babel helper calls by runtime helper imports. It is impossible to achieve this on lib version where the helpers are inlined.

Here is a brief summary on the number of inlined function _interopRequireDefault(obj) declarations in the artifacts. (produced by this script, lower is better)

	7.7.1	This branch
@babel/standalone	151	4
@babel/preset-env-standalone	101	0

Note that there are still 4 inlined _interopRequireDefault declaration not removed in @babel/standalone, all of which comes from third party dependencies, i.e. regenerator-runtime.

[buildsize]

File name	Previous Size	New Size	Change
babel-preset-env.js	2.78 MB	2.81 MB	29.12 KB (1%)
babel-preset-env.min.js	1.67 MB	1.63 MB	-46.82 KB (3%)
babel.js	2.96 MB	2.91 MB	-49.49 KB (2%)
babel.min.js	1.63 MB	1.56 MB	-74.19 KB (4%)

[JLHwung]

The size change of babel-preset-env.js comes from forceAllTransforms: true. I have removed forceAllTransform: true because standalone should build with default env targets.

The size change of babel-preset-env.js comes from bloated webpack injected comments like // CONCATENATED MODULE blablabla. The minified size change does support that we are shipping less code than the control branch.

[nicolo-ribaudo]

I don't like this 😆

Is it possible to use webpack's resolve instead?

[JLHwung]

By using resolve.alias like the other packages, webpack will ignore the browsers field in package.json.

[nicolo-ribaudo]

I'm not sure I follow. If we did something like this, wouldn't it work?

resolve: {
  alias: {
    "@babel/core$": "packages/babel-core/src/index.js"
  }
}

[hg-pyun]

It's a simple question. What is the advantage of declaring within this scope rather than at the top?

[JLHwung]

Not a strong reason: require("path") is used only when building babel-*-standalone. However, this config is shared with other building process (build/jest), by doing so we could avoid the overhead of requiring a builtin module.