refactor(@angular/build): extract karma application builder into smaller modules

The main `application_builder.ts` file was becoming too large and difficult to navigate. This change extracts several logical components into their own dedicated files:

- Karma asset middleware
- Karma polyfills plugin
- Karma progress reporter
- Code coverage utilities
- Karma configuration helpers
- General utility functions

This improves the overall code structure, making it easier to understand, test, and maintain.

Author: clydin