add individual polyfill files (#5584)

* add individual polyfill files

* rename files

* use preset-env for the script [skip ci]

packages/babel-polyfill/scripts/make-separate-polyfill-files.js

@@ -0,0 +1,21 @@
+"use strict";
+
+const fs = require("fs");
+const path = require("path");
+
+function relative(loc) {
+  return path.join(__dirname, "..", loc);
+}
+
+const builtIns = require("babel-preset-env/data/built-ins.json");
+const polyfills = Object.keys(builtIns);
+
+polyfills.concat([
+  "web.timers",
+  "web.immediate",
+  "web.dom.iterable"]
+).forEach((polyfill) => {
+  fs.writeFileSync(relative(`src/core-js/modules/${polyfill}.js`), `require("core-js/modules/${polyfill}");`);
+});
+
+fs.writeFileSync(relative("src/regenerator-runtime/runtime.js"), "require(\"regenerator-runtime/runtime\");");