convert @babel/cli to typescript (#13213)

* babel-cli flowts rename

* babel-cli flowts convert

* babel-cli

* yarn install

packages/babel-cli/src/babel-external-helpers.ts

@@ -0,0 +1,30 @@
+import commander from "commander";
+import { buildExternalHelpers } from "@babel/core";
+
+function collect(
+  value: string | any,
+  previousValue: Array<string>,
+): Array<string> {
+  // If the user passed the option with no value, like "babel-external-helpers --whitelist", do nothing.
+  if (typeof value !== "string") return previousValue;
+
+  const values = value.split(",");
+
+  return previousValue ? previousValue.concat(values) : values;
+}
+
+commander.option(
+  "-l, --whitelist [whitelist]",
+  "Whitelist of helpers to ONLY include",
+  collect,
+);
+commander.option(
+  "-t, --output-type [type]",
+  "Type of output (global|umd|var)",
+  "global",
+);
+
+commander.usage("[options]");
+commander.parse(process.argv);
+
+console.log(buildExternalHelpers(commander.whitelist, commander.outputType));