fix(@angular-devkit/build-angular): allow package file loader option with Vite prebundling

[clydin]

Previously, the application builder would consider all imports originating from a package to be considered external when caching was enabled. This allows Vite's prebundling to function and optimize the build/rebuild experience for the development server. However, when using the newly introduced loader option, this also inadvertently caused files that should be affected by the option that originate from a package to also be considered external. This behavior would then prevent the loader customization from being performed. To rectify this situation, all files that would be affected by a loader customization will not be marked as external for the purposes of prebundling unless explicitly configured by the externalDependencies option.

Closes #26866