[Proposal] Make able to write React in Typescript (#16210)

Co-authored-by: berlysia <berlysia@gmail.com>
Co-authored-by: fusagiko / takayamaki <takayamaki@users.noreply.github.com>

tsconfig.json

@@ -0,0 +1,13 @@
+{
+  "compilerOptions": {
+    "jsx": "react",
+    "target": "esnext",
+    "moduleResolution": "node",
+    "allowJs": true,
+    "noEmit": true,
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true
+  },
+  "include": ["app/javascript/mastodon", "app/javascript/packs"]
+}