Throw an error if client builds retain references to `*.server.ts` files

### Command

build

### Description

When SSR is enabled in an Angular project, there are a few `.server.ts` files produced (e.g. `app.config.server.ts`). The `.server.ts` suffix is also used by different applications as a way to structure and separate client and server code.

The proposal is to update the build pipeline to throw an error in case files with `.server.ts` suffix are present in the final client build output.

// cc @alan-agius4

Start with the Angular CLI build command and trace how the final client build output is produced when SSR is enabled. Verify how `.server.ts` files are retained in that output; done means the build reports an error whenever such a file is present.

Written by the indexing model from the issue text.