Interestingly enough, our rollup bundle optimization pipeline
did not work properly before 1b827b058e5060963590628d4735e6ac83c6dfdd.
Unused declarations were not elided because build optimizer did not
consider the Angular packages as side-effect free. Build optimizer has
a hard-coded list of Angular packages that are considered side-effect
free. Though this one did not match in the old version of the rollup
bundle rule, as internal sources were resolved through their resolved
bazel-out paths. Hence build optimizer could not detect the known
Angular framework packages. Now though, since we leverage the
Bazel-idiomatic `@bazel/rollup` implementation, sources are resolved
through linked `node_modules`, and build optimizer is able to properly
detect files as side-effect free.
PR Close#37623
fd65958b88