Move some build steps to gulp (#12127)

* chore: move generate-standalone to gulp tasks

* move build-flow-typings to gulp tasks

* chore: move build-typescript-typings to gulp tasks

* move generate-type-helpers to gulp tasks

* chore: include build-typings and generate-type-helpers in gulp build

* update generate-standalone comments

* address review comments

* chore: revert build-typings refactor

* fix: run build-typings in build-no-bundle

scripts/utils/writeFileAndMkDir.js

@@ -1,14 +0,0 @@
-const fs = require("fs");
-const path = require("path");
-
-module.exports = function writeFileAndMkDir(file, content) {
-  try {
-    fs.mkdirSync(path.dirname(file));
-  } catch (error) {
-    if (error.code !== "EEXIST") {
-      throw error;
-    }
-  }
-
-  fs.writeFileSync(file, content);
-};