Refactor: Use String.prototype.replaceAll() and update TS lib

- Replaces the custom `replaceAll` implementation in `packages/server/src/tools/edit.ts` with the standard `String.prototype.replaceAll()`.
- Updates `packages/server/tsconfig.json` to include `ES2021` in the `lib` compiler options to ensure TypeScript recognizes this method. This aligns with the project's Node.js version requirements \(Node.js 16.x+\).

Fixes https://github.com/google-gemini/gemini-cli/issues/7

packages/server/tsconfig.json

@@ -2,7 +2,7 @@
   "extends": "../../tsconfig.json",
   "compilerOptions": {
     "outDir": "dist",
-    "lib": ["DOM", "DOM.Iterable", "ES2020"],
+    "lib": ["DOM", "DOM.Iterable", "ES2021"],
     "composite": true
   },
   "include": ["index.ts", "src/**/*.ts", "src/**/*.json"],