For #271167
This makes it so our built-in extensions can mostly be built using `tsc` on the command line. Previously the extensions were picking up a lot of typing info from the root `node_modules` that meant they weren't truly independent
**Problem**
All of our extensions currently are built using the dom typings. This can lead to runtime errors if you mistakenly use `window` or similar
**Fix**
Exclude the dom typings from compile. Then explicitly import the node types for `URL` and `TextEncoder`
