remove proposals polyfills from default import [skip ci]

[hzoo]

Q	A
Fixed Issues?	Fixes #8416
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

The default import is replaced with only polyfills that are Stage 4, instead of also including the Stage < 4 polyfills. This should be in alignment with how we have removed the Stage presets. This also would mean we would need to add new imports when necessary.

And it sounds like we desire to also add the polyfill proposals individually? There's a maintenance cost to that too (not that bad) but then I wonder why we aren't just linking to the polyfill to use (that would just mean removing babel/polyfill as a package, as people may want to use other polyfills too) since we are just aliasing it. So do we really want to do this?

---

For the proposals in v2:

```js // require('../modules/es7.array.includes'); require('../modules/es7.array.flat-map'); require('../modules/es7.array.flatten'); require('../modules/es7.string.at'); // require('../modules/es7.string.pad-start'); // require('../modules/es7.string.pad-end'); require('../modules/es7.string.trim-left'); require('../modules/es7.string.trim-right'); require('../modules/es7.string.match-all'); // require('../modules/es7.symbol.async-iterator'); require('../modules/es7.symbol.observable'); // require('../modules/es7.object.get-own-property-descriptors'); // require('../modules/es7.object.values'); // require('../modules/es7.object.entries'); require('../modules/es7.object.define-getter'); require('../modules/es7.object.define-setter'); require('../modules/es7.object.lookup-getter'); require('../modules/es7.object.lookup-setter'); require('../modules/es7.map.to-json'); require('../modules/es7.set.to-json'); require('../modules/es7.map.of'); require('../modules/es7.set.of'); require('../modules/es7.weak-map.of'); require('../modules/es7.weak-set.of'); require('../modules/es7.map.from'); require('../modules/es7.set.from'); require('../modules/es7.weak-map.from'); require('../modules/es7.weak-set.from'); require('../modules/es7.global'); require('../modules/es7.system.global'); require('../modules/es7.error.is-error'); require('../modules/es7.math.clamp'); require('../modules/es7.math.deg-per-rad'); require('../modules/es7.math.degrees'); require('../modules/es7.math.fscale'); require('../modules/es7.math.iaddh'); require('../modules/es7.math.isubh'); require('../modules/es7.math.imulh'); require('../modules/es7.math.rad-per-deg'); require('../modules/es7.math.radians'); require('../modules/es7.math.scale'); require('../modules/es7.math.umulh'); require('../modules/es7.math.signbit'); // require('../modules/es7.promise.finally'); require('../modules/es7.promise.try'); require('../modules/es7.reflect.define-metadata'); require('../modules/es7.reflect.delete-metadata'); require('../modules/es7.reflect.get-metadata'); require('../modules/es7.reflect.get-metadata-keys'); require('../modules/es7.reflect.get-own-metadata'); require('../modules/es7.reflect.get-own-metadata-keys'); require('../modules/es7.reflect.has-metadata'); require('../modules/es7.reflect.has-own-metadata'); require('../modules/es7.reflect.metadata'); require('../modules/es7.asap'); require('../modules/es7.observable'); ```

from logan:

// Stage 3
import "core-js/fn/string/trim-left";
import "core-js/fn/string/trim-right";
import "core-js/fn/string/match-all";
import "core-js/fn/array/flat-map";
import "core-js/fn/array/flatten";  // RENAMED
import "core-js/fn/global";

// Stage 1
import "core-js/fn/symbol/observable";
import "core-js/fn/promise/try";
import "core-js/fn/observable";

// Stage 1 Math Extensions
import "core-js/fn/math/clamp";
import "core-js/fn/math/deg-per-rad";
import "core-js/fn/math/degrees";
import "core-js/fn/math/fscale";
import "core-js/fn/math/iaddh";
import "core-js/fn/math/isubh";
import "core-js/fn/math/imulh";
import "core-js/fn/math/rad-per-deg";
import "core-js/fn/math/radians";
import "core-js/fn/math/scale";
import "core-js/fn/math/umulh";
import "core-js/fn/math/signbit";

// Stage 1 "of and from on collection constructors"
import "core-js/fn/map/of";
import "core-js/fn/set/of";
import "core-js/fn/weak-map/of";
import "core-js/fn/weak-set/of";
import "core-js/fn/map/from";
import "core-js/fn/set/from";
import "core-js/fn/weak-map/from";
import "core-js/fn/weak-set/from";

// Stage 0
import "core-js/fn/string/at";

// Nonstandard
import "core-js/fn/object/define-getter";
import "core-js/fn/object/define-setter";
import "core-js/fn/object/lookup-getter";
import "core-js/fn/object/lookup-setter";
// import "core-js/fn/map/to-json"; // Not available standalone
// import "core-js/fn/set/to-json"; // Not available standalone

import "core-js/fn/system/global";
import "core-js/fn/error/is-error";
import "core-js/fn/asap";


// Decorator metadata? Not sure of stage/proposal
import "core-js/fn/reflect/define-metadata";
import "core-js/fn/reflect/delete-metadata";
import "core-js/fn/reflect/get-metadata";
import "core-js/fn/reflect/get-metadata-keys";
import "core-js/fn/reflect/get-own-metadata";
import "core-js/fn/reflect/get-own-metadata-keys";
import "core-js/fn/reflect/has-metadata";
import "core-js/fn/reflect/has-own-metadata";
import "core-js/fn/reflect/metadata";

write-polyfills.js

var a = ["core-js/fn/string/trim-left",
"core-js/fn/string/trim-right",
"core-js/fn/string/match-all",
"core-js/fn/array/flat-map",
"core-js/fn/array/flatten",
"core-js/fn/global",
"core-js/fn/symbol/observable",
"core-js/fn/promise/try",
"core-js/fn/observable",
"core-js/fn/math/clamp",
"core-js/fn/math/deg-per-rad",
"core-js/fn/math/degrees",
"core-js/fn/math/fscale",
"core-js/fn/math/iaddh",
"core-js/fn/math/isubh",
"core-js/fn/math/imulh",
"core-js/fn/math/rad-per-deg",
"core-js/fn/math/radians",
"core-js/fn/math/scale",
"core-js/fn/math/umulh",
"core-js/fn/math/signbit",
"core-js/fn/map/of",
"core-js/fn/set/of",
"core-js/fn/weak-map/of",
"core-js/fn/weak-set/of",
"core-js/fn/map/from",
"core-js/fn/set/from",
"core-js/fn/weak-map/from",
"core-js/fn/weak-set/from",
"core-js/fn/string/at"];

const fse = require('fs-extra');

Promise.all(a.map((file) => {
	return fse.outputFile(`${file.slice(11)}.js`, `import "${file}";`)
	.catch((error) => {
	    console.log(error)
	});
}))

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/8779/

[hzoo]

We should also update polyfill docs and also add this change to the upgrade doc.

[stnwk]

So, how do we include polyfills for @babel/plugin-proposal-x now? There is no documentation for this yet + the blog post https://babeljs.io/docs/en/next/v7-migration is too unspecific :/

Any input would be great! @hzoo

[nicolo-ribaudo]

You should import then directy from the core-js package.

e.g.

import "core-js/fn/array/flatMap";

[hzoo]

Ok I updated it a bit as well babel/website@3db6772

[stnwk]

Awesome, thank you both!