Revert "[PM-14485] Remove manifest and index.html logic from gulp" (#12032)

This reverts commit c388697fdf.

apps/browser/webpack/manifest.js

@@ -1,72 +0,0 @@
-/**
- * Transform the manifest template into a browser specific manifest.
- *
- * We support a simple browser prefix to the manifest keys. Example:
- *
- * ```json
- * {
- *   "name": "Default name",
- *   "__chrome__name": "Chrome override"
- * }
- * ```
- *
- * Will result in the following manifest:
- *
- * ```json
- * {
- *  "name": "Chrome override"
- * }
- * ```
- *
- * for Chrome.
- */
-function transform(browser) {
-  return (buffer) => {
-    let manifest = JSON.parse(buffer.toString());
-
-    manifest = transformPrefixes(manifest, browser);
-
-    return JSON.stringify(manifest, null, 2);
-  };
-}
-
-const browsers = ["chrome", "edge", "firefox", "opera", "safari"];
-
-/**
- * Flatten the browser prefixes in the manifest.
- *
- * - Removes unrelated browser prefixes.
- * - A null value deletes the non prefixed key.
- */
-function transformPrefixes(manifest, browser) {
-  const prefix = `__${browser}__`;
-
-  function transformObject(obj) {
-    return Object.keys(obj).reduce((acc, key) => {
-      // Determine if we need to recurse into the object.
-      const nested = typeof obj[key] === "object" && obj[key] !== null && !Array.isArray(obj[key]);
-
-      if (key.startsWith(prefix)) {
-        const newKey = key.slice(prefix.length);
-
-        // Null values are used to remove keys.
-        if (obj[key] == null) {
-          delete acc[newKey];
-          return acc;
-        }
-
-        acc[newKey] = nested ? transformObject(obj[key]) : obj[key];
-      } else if (!browsers.some((b) => key.startsWith(`__${b}__`))) {
-        acc[key] = nested ? transformObject(obj[key]) : obj[key];
-      }
-
-      return acc;
-    }, {});
-  }
-
-  return transformObject(manifest);
-}
-
-module.exports = {
-  transform,
-};