Add TypeScript 4.x as peerDependency to react-scripts

Created by: sheepsteak

CRA is supposed to officially support TypeScript 4 as of 4.0.0 but react-scripts is still set at only allowing TypeScript as ^3.2.1. As the CRA TypeScript template comes with TypeScript 4 I think this is causing an install error for users on npm 7 as it now attempts to install peerDependencies by default but the TypeScript versions conflict.

If CRA now supports TypeScript 4 I think this is the correct change to make things right.

Closes #9892 (closed) Closes #9764 (closed) (not really related to this but it can close after this) Closes #9995 (closed)

packages/react-scripts/package.json

@@ -94,7 +94,7 @@
     "fsevents": "^2.1.3"
   },
   "peerDependencies": {
-    "typescript": "^3.2.1"
+    "typescript": "^3.2.1 || ^4"
   },
   "peerDependenciesMeta": {
     "typescript": {