build: run closure-compiler (#3789)

* build: run closure-compiler

* Adds a script that runs the closure-compiler against the devapp / demo-app.
* The script will run on the CI as a new mode. Ensuring that all our components are closure-compatible.

Fixes #1206.

* Address feedback

scripts/ci/sources/mode.sh

@@ -13,6 +13,10 @@ is_aot() {
   [[ "$MODE" = aot ]]
 }
 
+is_closure_compiler() {
+  [[ "$MODE" = closure-compiler ]]
+}
+
 is_payload() {
   [[ "$MODE" = payload ]]
 }