build(aio): IDEs should only parse the `src` files

I found that VS Code was taking an age to bring up the intellisense
for TypeScript source files in the `aio/src` folder.
I believe that this is because it was trying to parse all the files in
the `aio/content/examples` folder as well, which is not relevant to the
web app development.

This change restricts the root `aio/tsconfig.json` to only the entry points
for the app, the unit tests and e2e tests.

aio/tsconfig.json

@@ -16,5 +16,12 @@
       "es2016",
       "dom"
     ]
-  }
+  },
+  "exclude": [
+    "content",
+    "tools",
+    "aio-builds-setup",
+    "node_modules",
+    "scripts"
+  ]
 }