Work towards getting isolated built-in extension compiles

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

extensions/typescript-language-features/tsconfig.json

@@ -2,6 +2,9 @@
 	"extends": "../tsconfig.base.json",
 	"compilerOptions": {
 		"outDir": "./out",
+		"typeRoots": [
+			"./node_modules/@types"
+		],
 		"esModuleInterop": true,
 		"types": [
 			"node"